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#1
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change from oil to Gas combi or stored water
I am thinking of changing from a warmflow bluebird oil boiler to gas but
don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. |
#2
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change from oil to Gas combi or stored water
curious wrote:
I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. I'm sure this is a subject on which there will be divided opinions, but mine is that stored cold and hot water is best, with both at low pressure of course. As far as I can see the only disadvantantages of this are that (1) low pressure means you can't have high pressure showers unless you either install a special pump or else go for an electrically heated shower which takes mains pressure water in, and (2) that you might lose some heat from a poorly insulated hot water tank to parts of the house which don't benefit from it. The only advantage of a combi is that it allows you to have high pressure hot water and does away with the need to have a HW tank. It takes just as long for water out of the hot tap to get hot, because water has to travel down the same distance of cold pipe before it gets from the source (be it the HW tank or the boiler itself) to the tap. The disadvantage of a combi is that it costs more, is more complicated, and there's more in it which can (and does) go wrong, and if you want a bath it'll probably take longer to fill than from a pre-heated tank, because the boiler can't heat it up as quickly as you want it to come out of the tap. A minor disadvantage is that if your house is already plumbed for low pressure hot water, and all your pipes, joints, and taps have been used to it for years/decades, then suddenly changing to higher pressure may invite latent leaks to read their heads. The risk is probably low, but not zero. I was once foolish enough to put one into a flat which previously had no central heating at all (open fireplaces or gas or electric fires only, cooking with gas, hot water by immersion heater). The installer suggested the "obvious" solution was to mount the boiler in the cupboard which then housed the HW tank, and to remove and discard the HW tank which would become redundant with a combi. I've regretted letting the salesman sell me a combi ever since, and I wouldn't have one now for all the tea in China. |
#3
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change from oil to Gas combi or stored water
On Jan 30, 2:40*pm, curious wrote:
I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. Combi boilers are slightly more efficient in that there is no hot water store. Hot water is generated "instantly." However they are complex and so tend to be less reliable. The hot water heat exchanger can scale up if your water is hard. They can be descaled chemically but all more expense. I would stick with your HW store and a condensing boiler. Put lots of insulation on your HW tank. |
#4
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change from oil to Gas combi or stored water
On 30/01/2011 14:40, curious wrote:
I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. Kostas -- Emails to this address are dropped. |
#5
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change from oil to Gas combi or stored water
On 30/01/2011 19:47, Kostas Kavoussanakis wrote:
I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. Indeed. Replacing a stored hot water system with a combi often involves a lot more plumbing changes than installing a replacement conventional boiler. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. If you are referring to a non-vented stored hot water system, this has a mains pressure cold feed to the hot cylinder rather than having a gravity feed from a cold storage tank. The advantage is that you get mains pressure hot water, and you don't have to accommodate a cold tank. The disadvantage is that, if the mains fails, you have no hot water - and you need a load of pressure limiting valves and (internal or external) expansion vessels - and the whole thing can only officially be installed and maintained by a suitably qualified person. -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#6
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change from oil to Gas combi or stored water
On Jan 30, 2:40*pm, curious wrote:
I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. Question 1 - Why do you want to move away from oil which is a fuel which can be easily shopped around for and if bought in summer is invariably cheaper Apart from our resident lunatic who simply parrots adverts he has read, most logical thinking people realise that a store of water gives you some security of supply if the mains goes off. If the storage tank is high enough you can operate a quite satisfactory shower and have the benefit of being able to fill a bath very quickly. If an immersin heater is fitted you also have an emergency heat alternative in the event of a failure of the primary heat source and you can (with a suitable cylinder or additional indirect coil) utilise solar heat for hot water contribution. There is even a feed in payment for hot water systems available now subject to meeting certain requirements. |
#7
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change from oil to Gas combi or stored water
John Rumm wrote:
On 30/01/2011 17:57, harry wrote: On Jan 30, 2:40 pm,curious wrote: I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. Combi boilers are slightly more efficient in that there is no hot water store. Can't see the relevance of that. Even if the hot water store loses heat into the house, its just heat that the CH side does not have to contribute later. There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps, but with a cylinder there are bigger losses unless you use all the hot water in the cylinder that you have produced. The losses from a cylinder contribute nothing to the CH side of things in the summer (if you remember them?) -- Adam |
#8
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change from oil to Gas combi or stored water
"cynic" wrote in message ... On Jan 30, 2:40 pm, curious wrote: I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. Question 1 - Why do you want to move away from oil which is a fuel which can be easily shopped around for and if bought in summer is invariably cheaper £260 for 500 litres at moment which lasts about 6 weeks in winter. Over Christmass and new year lasted only 4 weeks. Another issue is the cold water storage tank in loft. This was replaced with a plastic/PVC one 20 years ago so how long do they last before needing replaced. Galvanised one was 25 years old when it needed replace. .. |
#9
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change from oil to Gas combi or stored water
On Mon, 31 Jan 2011 15:36:07 -0000, curious wrote:
£260 for 500 litres at moment which lasts about 6 weeks in winter. Over Christmass and new year lasted only 4 weeks. Pah, bought 1000l on 14 Dec, bought another 1000l on 20 Jan and for more than your 52p/l inc VAT. B-( BTW 1000 and 2000l is quite often a break point in discount, our supplier will normally knock 1p/l off for 2000l and "negociate" for 1000l. Another issue is the cold water storage tank in loft. This was replaced with a plastic/PVC one 20 years ago so how long do they last before needing replaced. There are ones in one of our lofts that are probably getting on for 30 years old. Plastic tanks, properly installed, out of sunlight last basically for ever. -- Cheers Dave. |
#10
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change from oil to Gas combi or stored water
"Dave Liquorice" wrote in message ll.co.uk... On Mon, 31 Jan 2011 15:36:07 -0000, curious wrote: £260 for 500 litres at moment which lasts about 6 weeks in winter. Over Christmass and new year lasted only 4 weeks. Pah, bought 1000l on 14 Dec, bought another 1000l on 20 Jan and for more than your 52p/l inc VAT. B-( BTW 1000 and 2000l is quite often a break point in discount, our supplier will normally knock 1p/l off for 2000l and "negociate" for 1000l. Another issue is the cold water storage tank in loft. This was replaced with a plastic/PVC one 20 years ago so how long do they last before needing replaced. There are ones in one of our lofts that are probably getting on for 30 years old. Plastic tanks, properly installed, out of sunlight last basically for ever. In December with temperatures of minus 15 and below and the heating pipes comming under the back garden I had the heating timed to come in for 15 minutes every 2 hours through the night to stop the pipes freezing, the oil in the feed pipe on my brothers boiler froze at point of entry to the garage. -- Cheers Dave. |
#11
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change from oil to Gas combi or stored water
On 30/01/2011 20:09, Roger Mills wrote:
On 30/01/2011 19:47, Kostas Kavoussanakis wrote: I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. Indeed. Replacing a stored hot water system with a combi often involves a lot more plumbing changes than installing a replacement conventional boiler. Thanks Roger. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. If you are referring to a non-vented stored hot water system, this has a mains pressure cold feed to the hot cylinder rather than having a gravity feed from a cold storage tank. The advantage is that you get mains pressure hot water, and you don't have to accommodate a cold tank. Ah, I thought that modern open-vent systems might pressurise the hot water. The disadvantage is that, if the mains fails, you have no hot water - and you need a load of pressure limiting valves and (internal or external) expansion vessels - and the whole thing can only officially be installed and maintained by a suitably qualified person. Great analysis, thanks. How complicated is it to convert from open-vented to sealed? I am thinking isolating the cold water tank and rerouting mains water, but there may well be more I haven't thought of. I am very limited by hardwood flooring and a single hatch near the boiler that, alas, has a dwarf-wall between it and the hot-water tank. Also, is it correct that with open-vented I don't have an expansion tank to inspect for water loss? I am thinking of relocating the boiler directly above its current location, which would impair access massively (unfloored loft and awkward, tri-bearing trusses). Cheers, Kostas (expecting this is useful to the OP as well) -- Emails to this address are dropped. |
#12
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change from oil to Gas combi or stored water
On 31/01/2011 20:36, Kostas Kavoussanakis wrote:
On 30/01/2011 20:09, Roger Mills wrote: On 30/01/2011 19:47, Kostas Kavoussanakis wrote: I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. Indeed. Replacing a stored hot water system with a combi often involves a lot more plumbing changes than installing a replacement conventional boiler. Thanks Roger. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. If you are referring to a non-vented stored hot water system, this has a mains pressure cold feed to the hot cylinder rather than having a gravity feed from a cold storage tank. The advantage is that you get mains pressure hot water, and you don't have to accommodate a cold tank. Ah, I thought that modern open-vent systems might pressurise the hot water. The disadvantage is that, if the mains fails, you have no hot water - and you need a load of pressure limiting valves and (internal or external) expansion vessels - and the whole thing can only officially be installed and maintained by a suitably qualified person. Great analysis, thanks. How complicated is it to convert from open-vented to sealed? I am thinking isolating the cold water tank and rerouting mains water, but there may well be more I haven't thought of. I am very limited by hardwood flooring and a single hatch near the boiler that, alas, has a dwarf-wall between it and the hot-water tank. Also, is it correct that with open-vented I don't have an expansion tank to inspect for water loss? I am thinking of relocating the boiler directly above its current location, which would impair access massively (unfloored loft and awkward, tri-bearing trusses). Cheers, Kostas (expecting this is useful to the OP as well) I fear that you may be confusing your water circuits! A house with a central heating and stored hot water system has two separate water circuits. The *primary* circuit connects the boiler to the radiators and to the indirect coil inside the domestic hot water cylinder. This can be vented or unvented (pressurised). If vented, there will be a small fill and expansion tank - usually in the attic. If unvented, there will be a filling loop with pressure gauge, a pressure relief valve (safety device) and an expansion vessel. Converting from vented to unvented is fairly straight-forward and involves removing the F&E tank and adding the other components mentioned above. Whether vented or unvented, the primary circuit keeps circulating the *same* water - and usually has corrosion inhibitor in it. The *secondary* circuit contains the water which flows to your hot taps, and is stored in a hot water cylinder. It is heated by water from the primary circuit which flows through a coil inside the cylinder, but doesn't mix with the secondary water (you wouldn't want to bath in inhibitor!). The secondary circuit can be vented or unvented. If vented, there will be large a cold water header tank which feeds cold water into the bottom of the hot cylinder to replace the hot water flowing to the taps. If unvented, the cold water feed to the cylinder comes from the mains rather than from a header tank - and you then need non-return valves, pressure limiting valves, an expansion vessel and an over-pressure relief valve. Converting from vented to unvented is a major operation because the hot cylinder has to be replaced with one which is capable of sustaining the much higher water pressure, in addition to adding the other components. As I mentioned in my previous post, this officially has to be installed by someone who is suitably qualified because there are lots of safety issues. Which circuit were you asking about? -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#13
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change from oil to Gas combi or stored water
On Jan 31, 8:36*pm, Kostas Kavoussanakis
wrote: On 30/01/2011 20:09, Roger Mills wrote: On 30/01/2011 19:47, Kostas Kavoussanakis wrote: I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. Indeed. Replacing a stored hot water system with a combi often involves a lot more plumbing changes than installing a replacement conventional boiler. Thanks Roger. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. If you are referring to a non-vented stored hot water system, this has a mains pressure cold feed to the hot cylinder rather than having a gravity feed from a cold storage tank. The advantage is that you get mains pressure hot water, and you don't have to accommodate a cold tank.. Ah, I thought that modern open-vent systems might pressurise the hot water. |
#14
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change from oil to Gas combi or stored water
On Sun, 30 Jan 2011 20:33:46 -0000, "ARWadsworth"
wrote: There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps Or more precisely there is lots more lukewarm, cold, and scalding hot water wasted in a combi installation and significantly more firings of the boiler. A typical scenario: Every time you turn the tap on you get bugger all hot water, by the time a combi has fired and water is flowing in the pipe to the tap then nine times out of ten you'll have thought f*ck it, I can't be bothered to wait this long for hot water. So you turn the tap off. Then some time later someone else turns the tap on, they get a spurt of lukewarm water, then cold, as the boiler fires up again on yet another wasted exercise. This goes on all through the day and all the boiler is achieving is a warming up of pipework. Then two people turn on a tap and get cold water then possibly lukewarm water, then one turns the tap off and a gush of almost scalding hot water comes out of the other tap. The only time you'll get continuous hot water is running a bath or taking a shower. The shower will work, but if someone else turns a tap on it could scald you or leave you covered in ice cold water. The bath might even fill before the boiler needs an annual service although you probably have to start filling it the moment the service person walks out the door. I'd sooner bathe in a tin bath in the middle of a snow covered field than ever have a combi. -- |
#15
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change from oil to Gas combi or stored water
The Other Mike wrote:
I'd sooner bathe in a tin bath in the middle of a snow covered field than ever have a combi. I tend to agree. Only way a combi REALLY works is if it is MASSIVELY oversized. Then its bloody inefficient at central heating usually. System boiler and either thermal store/header tank or pressurized tank is the sane way to go. Unless you are a tiny 1 bedroom place. |
#16
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change from oil to Gas combi or stored water
The Other Mike wrote:
On Sun, 30 Jan 2011 20:33:46 -0000, "ARWadsworth" wrote: There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps Or more precisely there is lots more lukewarm, cold, and scalding hot water wasted in a combi installation and significantly more firings of the boiler. A typical scenario: Every time you turn the tap on you get bugger all hot water, by the time a combi has fired and water is flowing in the pipe to the tap then nine times out of ten you'll have thought f*ck it, I can't be bothered to wait this long for hot water. So you turn the tap off. Then some time later someone else turns the tap on, they get a spurt of lukewarm water, then cold, as the boiler fires up again on yet another wasted exercise. This goes on all through the day and all the boiler is achieving is a warming up of pipework. Then two people turn on a tap and get cold water then possibly lukewarm water, then one turns the tap off and a gush of almost scalding hot water comes out of the other tap. A well located combi makes a big difference. Mine is in the kitchen near to the sink and the bathroom is just above it. The installations where the combi is 12m away from the taps are a waste of time, water and gas. The only time you'll get continuous hot water is running a bath or taking a shower. The shower will work, but if someone else turns a tap on it could scald you or leave you covered in ice cold water. The bath might even fill before the boiler needs an annual service although you probably have to start filling it the moment the service person walks out the door. That depends on when you want a bath and if you are prepared to heat up the water and risk not using it. I get in from work at different times. Sometimes I want a bath as soon as I get in, sometimes I don't. All I have to to is turn the bathtap on and wait 10 minutes and at no point do I ever waste a tankfull of hot water. You don't have to stand and watch the bath fill any more than you need to stand next to the airing cupboard and wait until the cylinder is hot. -- Adam |
#17
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change from oil to Gas combi or stored water
On 01/02/2011 00:36, Roger Mills wrote:
On 31/01/2011 20:36, Kostas Kavoussanakis wrote: On 30/01/2011 20:09, Roger Mills wrote: On 30/01/2011 19:47, Kostas Kavoussanakis wrote: I too am considering the options in case my 25-yo boiler gives up the ghost. The combi needs good pressure mains, I believe; have you got it? It looks like, if you are upgrading or replacing (as opposed to installing fresh), the combi is the most drastic option. Indeed. Replacing a stored hot water system with a combi often involves a lot more plumbing changes than installing a replacement conventional boiler. Thanks Roger. I see from the wiki and from the Vaillant and Worcester websites that there are two non-combi options: open-vent (the same as what you and I have) and sealed system (which only does away with the cold-water tank). I am still not clear of the benfits of each set-up, so I will stop here. If you are referring to a non-vented stored hot water system, this has a mains pressure cold feed to the hot cylinder rather than having a gravity feed from a cold storage tank. The advantage is that you get mains pressure hot water, and you don't have to accommodate a cold tank. Ah, I thought that modern open-vent systems might pressurise the hot water. The disadvantage is that, if the mains fails, you have no hot water - and you need a load of pressure limiting valves and (internal or external) expansion vessels - and the whole thing can only officially be installed and maintained by a suitably qualified person. Great analysis, thanks. How complicated is it to convert from open-vented to sealed? I am thinking isolating the cold water tank and rerouting mains water, but there may well be more I haven't thought of. I am very limited by hardwood flooring and a single hatch near the boiler that, alas, has a dwarf-wall between it and the hot-water tank. Also, is it correct that with open-vented I don't have an expansion tank to inspect for water loss? I am thinking of relocating the boiler directly above its current location, which would impair access massively (unfloored loft and awkward, tri-bearing trusses). I fear that you may be confusing your water circuits! A house with a central heating and stored hot water system has two separate water circuits. The *primary* circuit connects the boiler to the radiators and to the indirect coil inside the domestic hot water cylinder. This can be vented or unvented (pressurised). If vented, there will be a small fill and expansion tank - usually in the attic. If unvented, there will be a filling loop with pressure gauge, a pressure relief valve (safety device) and an expansion vessel. Converting from vented to unvented is fairly straight-forward and involves removing the F&E tank and adding the other components mentioned above. Whether vented or unvented, the primary circuit keeps circulating the *same* water - and usually has corrosion inhibitor in it. The *secondary* circuit contains the water which flows to your hot taps, and is stored in a hot water cylinder. It is heated by water from the primary circuit which flows through a coil inside the cylinder, but doesn't mix with the secondary water (you wouldn't want to bath in inhibitor!). The secondary circuit can be vented or unvented. If vented, there will be large a cold water header tank which feeds cold water into the bottom of the hot cylinder to replace the hot water flowing to the taps. If unvented, the cold water feed to the cylinder comes from the mains rather than from a header tank - and you then need non-return valves, pressure limiting valves, an expansion vessel and an over-pressure relief valve. Converting from vented to unvented is a major operation because the hot cylinder has to be replaced with one which is capable of sustaining the much higher water pressure, in addition to adding the other components. As I mentioned in my previous post, this officially has to be installed by someone who is suitably qualified because there are lots of safety issues. Which circuit were you asking about? Thanks again, Roger (and harry too). I was unaware of the details of the two different cold tanks; do I really have a small F&E tank in the attic? I can't see it, but it's probably on the unfloored side of the big tank. I have no idea which circuit I am (they are) talking about, all I wanted to figure out is what kind of boiler I should be looking at. I am now guessing this is about the primary circuit, shall we establish? Let me use Vaillant terminology, as per the following: http://www.vaillant.co.uk/installers...ncy-boilers-2/ I am discounting combis. I like the fact that I know nothing about this F&E tank and have nothing to maintain. Does this mean that I am looking at open-vent boilers? What is the benefit of a vented primary circuit? Re pressurised secondary circuits: am I right that they are possible with both open-vent and system boilers? Also, I had a look at prices for the Vaillant tanks and the eyes watered, even without the big job you and harry mentioned. What does one get in return? You suggested "mains pressure hot water, and you don't have to accommodate a cold tank." I don't mind the latter; can one get a similar effect to the former by installing a wee pump close to a gravity-fed HW tank? Any other benefits? Thanks, Kostas -- Emails to this address are dropped. |
#18
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change from oil to Gas combi or stored water
On 02/02/2011 12:30, ARWadsworth wrote:
You don't have to stand and watch the bath fill any more than you need to stand next to the airing cupboard and wait until the cylinder is hot. A thermostat will turn off the source of heat when the tank is hot. What stops your bath from overflowing if you go away and forget about it? -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#19
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change from oil to Gas combi or stored water
John Rumm wrote:
On 02/02/2011 11:52, The Other Mike wrote: On Sun, 30 Jan 2011 20:33:46 -0000, "ARWadsworth" wrote: There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps Or more precisely there is lots more lukewarm, cold, and scalding hot water wasted in a combi installation and significantly more firings of the boiler. A typical scenario: Every time you turn the tap on you get bugger all hot water, by the time a combi has fired and water is flowing in the pipe to the tap then nine times out of ten you'll have thought f*ck it, I can't be bothered to wait this long for hot water. So you turn the tap off. This was part of my point about people buying NuTool style combis. Decent ones have a store of a couple of litres of hot water they keep sat at temperature, and which they can blend into the water at startup. Hence they deliver hot water from the get go. The only time you'll get continuous hot water is running a bath or taking a shower. The shower will work, but if someone else turns a tap on it could scald you or leave you covered in ice cold water. The bath might even fill before the boiler needs an annual service although you probably have to start filling it the moment the service person walks out the door. I'd sooner bathe in a tin bath in the middle of a snow covered field than ever have a combi. I would sooner have a hot water system that works properly than a badly implemented one that doesn't. "Combi = bad / anything else = good" just shows a lack of experience of decent combis, or badly executed alternative systems. Combis certainly have limitations, but then again so do storage systems. Its a case of making a sensible decision about what is appropriate for the circumstance. Yebbut if you execute a combi properly (sic!) it ends up taking more space and costing more than a conventional boiler and tank :-) |
#20
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change from oil to Gas combi or stored water
On 02/02/2011 19:03, Kostas Kavoussanakis wrote:
Thanks again, Roger (and harry too). I was unaware of the details of the two different cold tanks; do I really have a small F&E tank in the attic? I can't see it, but it's probably on the unfloored side of the big tank. You *might* have a sealed (unvented) primary system - in which case there wouldn't be an F&E tank. Have you got an expansion vessel anywhere? I have no idea which circuit I am (they are) talking about Sadly, neither have they! , all I wanted to figure out is what kind of boiler I should be looking at. I am now guessing this is about the primary circuit, shall we establish? Let me use Vaillant terminology, as per the following: http://www.vaillant.co.uk/installers...ncy-boilers-2/ The terminology used by Vaillant in that reference is very confusing and ambiguous - so I'm not surprised that you are confused! The primary and secondary circuits can each independently be either vented or non-venting - giving four possibilities - whereas Vaillant give the impression that it's all or nothing. The most common current domestic arrangement is a non-vented primary and vented secondary circuit. You could almost certainly achieve that with either of Vaillant's so called Heating Only or System boilers. The only difference would be that the system boiler would have the pump and pressure vessel inside the boiler casing whereas the Heating Only boiler would require these to be installed external to the boiler. The system boiler saves space - and some plumbing - but the pump and pressure vessel are probably then proprietary, and more difficult and expensive to replace. I am discounting combis. Good! I like the fact that I know nothing about this F&E tank and have nothing to maintain. Does this mean that I am looking at open-vent boilers? What is the benefit of a vented primary circuit? No. A vented primary circuit DOES have an F&E tank. An unvented system has a pressure vessel and filling loop instead. You would still have to maintain *that* in terms of checking the pressure periodically and topping up if necessary - just as you have to check the level in an F&E tank. Others have already explained the pros and cons in terms of adding inhibitor, pumping over, etc. Generally, non-vented primary circuits are preferable. Re pressurised secondary circuits: am I right that they are possible with both open-vent and system boilers? Yes. Also, I had a look at prices for the Vaillant tanks and the eyes watered, even without the big job you and harry mentioned. What does one get in return? You suggested "mains pressure hot water, and you don't have to accommodate a cold tank." I don't mind the latter; can one get a similar effect to the former by installing a wee pump close to a gravity-fed HW tank? Any other benefits? Because non-vented cylinders have to sustain mains pressure, they are built like the proverbial brick s**thouse - and probably last for ever. But they *do* require expert installation and regular maintenance - and you get no hot water if there's a mains water supply failure. You can indeed fit a boost pump on the hot water outlet (NOT the cold water inlet!) of the hot cylinder, increasing the flow rate to the taps. This would usually be controlled by a flow switch so that it would only operate when you open a hot tap. It wouldn't be silent, of course, but shouldn't be too intrusive. -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#21
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change from oil to Gas combi or stored water
"Roger Mills" wrote in message
... On 02/02/2011 12:30, ARWadsworth wrote: You don't have to stand and watch the bath fill any more than you need to stand next to the airing cupboard and wait until the cylinder is hot. A thermostat will turn off the source of heat when the tank is hot. What stops your bath from overflowing if you go away and forget about it? I have not got dementia. I can remember to turn a tap off. -- Adam |
#22
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change from oil to Gas combi or stored water
On Feb 2, 11:23*pm, John Rumm wrote:
On 02/02/2011 11:52, The Other Mike wrote: On Sun, 30 Jan 2011 20:33:46 -0000, "ARWadsworth" *wrote: There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps Or more precisely there is lots more lukewarm, cold, and scalding hot water wasted in a combi installation and significantly more firings of the boiler. A typical scenario: Every time you turn the tap on you get bugger all hot water, by the time a combi has fired and water is flowing in the pipe to the tap then nine times out of ten you'll have thought f*ck it, I can't be bothered to wait this long for hot water. So you turn the tap off. This was part of my point about people buying NuTool style combis. Decent ones have a store of a couple of litres of hot water they keep sat at temperature, and which they can blend into the water at startup. Hence they deliver hot water from the get go. The only time you'll get continuous hot water is running a bath or taking a shower. *The shower will work, but if someone else turns a tap on it could scald you or leave you covered in ice cold water. The bath might even fill before the boiler needs an annual service although you probably have to start filling it the moment the service person walks out the door. I'd sooner bathe in a tin bath in the middle of a snow covered field than ever have a combi. I would sooner have a hot water system that works properly than a badly implemented one that doesn't. "Combi = bad / anything else = good" just shows a lack of experience of decent combis, I've had the misfortune to encounter at least 8 combi systems over the years. Not one of them was a patch on even a mediocre stored hot water system (with addition of pumped showers). One or two I could accept as bad examples but 8/8 tells me there is no such thing as a good combi installation. MBQ |
#23
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change from oil to Gas combi or stored water
On Jan 30, 6:09*pm, John Rumm wrote:
On 30/01/2011 14:40, curious wrote: I am thinking of changing from a warmflow bluebird oil boiler to gas but don't know whether to go for a combi gas boiler or stay with my current setup of stored hot and cold water. We had a water cut of 3 days in the new year and stored water was a blessing so what are the main advantages of a combi. Gas heating is still in the minority in Northern Ireland at the moment but catchingup. The primary question is: does your current hot water system work well enough and meet your needs? If the answer is yes, then using a gas heating only or a system boiler will involve least expense and hassle. On the plus side combis are cheap and easy to install from scratch (but that is rarely relevant when retrofitting to an existing system). They may also save space in some cases. They do very good showers without need for pumps etc. s/very good/adequate/ MBQ |
#24
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change from oil to Gas combi or stored water
On Jan 31, 4:10*pm, "Dave Liquorice"
wrote: On Mon, 31 Jan 2011 15:36:07 -0000, curious wrote: £260 for 500 litres at moment which lasts about 6 weeks in winter. Over Christmass and new year lasted only 4 weeks. Pah, bought 1000l on 14 Dec, bought another 1000l on 20 Jan and for more than your 52p/l inc VAT. *B-( *BTW 1000 and 2000l is quite often a break point in discount, our supplier will normally knock 1p/l off for 2000l and "negociate" for 1000l. Another issue is the cold water storage tank in loft. This was replaced with a plastic/PVC one 20 years ago so how long do they last before needing replaced. There are ones in one of our lofts that are probably getting on for 30 years old. Plastic tanks, properly installed, out of sunlight last basically for ever. Ours are 38 years old. MBQ |
#25
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change from oil to Gas combi or stored water
Man at B&Q wrote:
On Feb 2, 11:23 pm, John Rumm wrote: On 02/02/2011 11:52, The Other Mike wrote: On Sun, 30 Jan 2011 20:33:46 -0000, "ARWadsworth" wrote: There is no "wasted hot water". There are of course the losses in the pipe work from the combi to the taps Or more precisely there is lots more lukewarm, cold, and scalding hot water wasted in a combi installation and significantly more firings of the boiler. A typical scenario: Every time you turn the tap on you get bugger all hot water, by the time a combi has fired and water is flowing in the pipe to the tap then nine times out of ten you'll have thought f*ck it, I can't be bothered to wait this long for hot water. So you turn the tap off. This was part of my point about people buying NuTool style combis. Decent ones have a store of a couple of litres of hot water they keep sat at temperature, and which they can blend into the water at startup. Hence they deliver hot water from the get go. The only time you'll get continuous hot water is running a bath or taking a shower. The shower will work, but if someone else turns a tap on it could scald you or leave you covered in ice cold water. The bath might even fill before the boiler needs an annual service although you probably have to start filling it the moment the service person walks out the door. I'd sooner bathe in a tin bath in the middle of a snow covered field than ever have a combi. I would sooner have a hot water system that works properly than a badly implemented one that doesn't. "Combi = bad / anything else = good" just shows a lack of experience of decent combis, I've had the misfortune to encounter at least 8 combi systems over the years. Not one of them was a patch on even a mediocre stored hot water system (with addition of pumped showers). One or two I could accept as bad examples but 8/8 tells me there is no such thing as a good combi installation. My sister had one in Germany. BUT it was in the basement, with a 5000 liter oil tank, and was the size of a small car. 60KW I believe. It was no better than my 12Kw system boiler and pressurised hot water tank, and more expensive, and took up more space. MBQ |
#26
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change from oil to Gas combi or stored water
On 03/02/2011 00:20, John Rumm wrote:
I would argue that the sealed system is the one to go for in most circumstances. Easier to implement, less space, easier and faster to fill and bleed, Are these of interest in my (and the OP's case) where we already have an old Y-plan system? Isn't it easier and cheaper to just stick a Heating Only boiler in place of the old one and be done with it? no risk of floods if you get a leak in the heating system etc. No sucking air into the system and no pump over. On the down side its a tad harder to add inhibitor since you can't just log it in a tank, but you will get less corrosion with a sealed system anyway usually. I don't meddle with these things and I have a local technican servicing my dinosaur annually anyway, so I guess no problem in my case. The Vaillant ones you were looking at can also interact with a boiler that has external temperature control. Ah, the Vaillant looks to my untrained eye as a problem in this department. The weather compensation module requires its matching compensator and (I think) an additional mixer module. This means that the boiler can use low flow temperatures for maximum efficiency when heating the house via the rads, but then switch to a higher temperature for reheating the tank so as to make best use of its capacity. Thanks for the input! Kostas -- Emails to this address are dropped. |
#27
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change from oil to Gas combi or stored water
On 03/02/2011 09:30, Roger Mills wrote:
On 02/02/2011 19:03, Kostas Kavoussanakis wrote: Thanks again, Roger (and harry too). I was unaware of the details of the two different cold tanks; do I really have a small F&E tank in the attic? I can't see it, but it's probably on the unfloored side of the big tank. You *might* have a sealed (unvented) primary system - in which case there wouldn't be an F&E tank. Have you got an expansion vessel anywhere? No idea. Never been told to keep an eye on anything. Does the F&E tank not fill up as needed with a cistern-type, floating-ball inlet? all I wanted to figure out is what kind of boiler I should be looking at. I am now guessing this is about the primary circuit, shall we establish? Let me use Vaillant terminology, as per the following: http://www.vaillant.co.uk/installers...ncy-boilers-2/ The terminology used by Vaillant in that reference is very confusing and ambiguous - so I'm not surprised that you are confused! The primary and secondary circuits can each independently be either vented or non-venting - giving four possibilities - whereas Vaillant give the impression that it's all or nothing. The most common current domestic arrangement is a non-vented primary and vented secondary circuit. You could almost certainly achieve that with either of Vaillant's so called Heating Only or System boilers. The only difference would be that the system boiler would have the pump and pressure vessel inside the boiler casing whereas the Heating Only boiler would require these to be installed external to the boiler. The system boiler saves space - and some plumbing - but the pump and pressure vessel are probably then proprietary, and more difficult and expensive to replace. I am discounting combis. Good! I like the fact that I know nothing about this F&E tank and have nothing to maintain. Does this mean that I am looking at open-vent boilers? What is the benefit of a vented primary circuit? No. A vented primary circuit DOES have an F&E tank. An unvented system has a pressure vessel and filling loop instead. You would still have to maintain *that* in terms of checking the pressure periodically and topping up if necessary - just as you have to check the level in an F&E tank. I used ambiguous language above, because I was under the impression I have nothing to do when an F&E tank is fitted. You can indeed fit a boost pump on the hot water outlet (NOT the cold water inlet!) of the hot cylinder, increasing the flow rate to the taps. This would usually be controlled by a flow switch so that it would only operate when you open a hot tap. It wouldn't be silent, of course, but shouldn't be too intrusive. Thanks. Modulo some minor points in this and my posting in response to John Rumm, I am now less scared of the day my boiler inevitably goes. I think that there is a simple, economical solution in the form of a heating-only ("open vent" as per Vaillant) boiler available. Kostas -- Emails to this address are dropped. |
#28
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change from oil to Gas combi or stored water
On Feb 3, 7:51*pm, Kostas Kavoussanakis
wrote: On 03/02/2011 00:20, John Rumm wrote: I would argue that the sealed system is the one to go for in most circumstances. Easier to implement, less space, easier and faster to fill and bleed, Are these of interest in my (and the OP's case) where we already have an old Y-plan system? Isn't it easier and cheaper to just stick a Heating Only boiler in place of the old one and be done with it? no risk of floods if you get a leak in the heating system etc. No sucking air into the system and no pump over. On the down side its a tad harder to add inhibitor since you can't just log it in a tank, but you will get less corrosion with a sealed system anyway usually. I don't meddle with these things and I have a local technican servicing my dinosaur annually anyway, so I guess no problem in my case. The Vaillant ones you were looking at can also interact with a boiler that has external temperature control. Ah, the Vaillant looks to my untrained eye as a problem in this department. The weather compensation module requires its matching compensator and (I think) an additional mixer module. This means that the boiler can use low flow temperatures for maximum efficiency when heating the house via the rads, but then switch to a higher temperature for reheating the tank so as to make best use of its capacity. Thanks for the input! Kostas -- Emails to this address are dropped. I as the original poster was looking for a cheaper alternative to oil with minimum disturbance. My concerns were the pvc cold water storage tank in the loft might need replacing as it is 20 years old and if I needed to do that I may as well go for something different either a combi or a system with hot water storage cylinder like the vaillant one. I live in a chalet bungalow with the bathroom down stairs bedrooms upstairs and cold water storage tank in loft so get very good pressure in the hot taps so mains pressure hot water is not a required so vented system would suit me. |
#29
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change from oil to Gas combi or stored water
On 03/02/2011 20:06, Kostas Kavoussanakis wrote:
On 03/02/2011 09:30, Roger Mills wrote: You *might* have a sealed (unvented) primary system - in which case there wouldn't be an F&E tank. Have you got an expansion vessel anywhere? No idea. Never been told to keep an eye on anything. Does the F&E tank not fill up as needed with a cistern-type, floating-ball inlet? The F&E tank *largely* looks after itself - using a ball-valve to top up when necessary. *However*, because the ball valve opens so infrequently, it can seize up - and not deliver water when required - with the result that the F&E tank empties, and air is drawn into the system. That's why it's a good idea to keep an eye on it periodically. -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#30
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change from oil to Gas combi or stored water
On Feb 3, 12:12*pm, "Man at B&Q" wrote:
On Jan 31, 4:10*pm, "Dave Liquorice" wrote: On Mon, 31 Jan 2011 15:36:07 -0000, curious wrote: £260 for 500 litres at moment which lasts about 6 weeks in winter. Over Christmass and new year lasted only 4 weeks. Pah, bought 1000l on 14 Dec, bought another 1000l on 20 Jan and for more than your 52p/l inc VAT. *B-( *BTW 1000 and 2000l is quite often a break point in discount, our supplier will normally knock 1p/l off for 2000l and "negociate" for 1000l. Another issue is the cold water storage tank in loft. This was replaced with a plastic/PVC one 20 years ago so how long do they last before needing replaced. There are ones in one of our lofts that are probably getting on for 30 years old. Plastic tanks, properly installed, out of sunlight last basically for ever. Ours are 38 years old. MBQ New thoughts I have seen reference to a Cabin Pack for outing oil boilers outside in a small purpose built housing. Can you get similar for gas boilers? |
#31
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change from oil to Gas combi or stored water
On 06/02/2011 15:08, curious wrote:
New thoughts I have seen reference to a Cabin Pack for outing oil boilers outside in a small purpose built housing. Can you get similar for gas boilers? Not a specialist, as you may have guessed, but I would be worried about condensate pipe freezing. Also, feeding it with gas may be a challenge, but I am sure others will chip in here. Kostas -- Emails to this address are dropped. |
#32
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change from oil to Gas combi or stored water
On Feb 8, 7:34*pm, Kostas Kavoussanakis
wrote: On 06/02/2011 15:08, curious wrote: New thoughts I have seen reference to a Cabin Pack for outing oil boilers outside in a small purpose built housing. Can you get similar for gas boilers? Not a specialist, as you may have guessed, but I would be worried about condensate pipe freezing. Also, feeding it with gas may be a challenge, but I am sure others will chip in here. Kostas -- Emails to this address are dropped. Just that the kitchen has been re done recently and there would be no room for a boiler but the detached garage has so a non combi in the garage would suit. But I see floor standing oil boilers for garage install but all gas seem to be geared to wall hanging in kitchens or airing cupboards. |
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