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Another combi boiler hot water question
I've been trying to understand what happens with the hot water when my
wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? -- AnthonyL |
Another combi boiler hot water question
On 08/03/2019 12:24, AnthonyL wrote:
I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? Has it always done this? As a mere user of the Baxi 105HE, not an engineer thereof, I'm wondering where the CH & Hot Water temperature knobs are set? Mine are set so the temperature never quite goes up to 70 (I was told to do this to reduce limescale deposits though I don't know if that really works.) I never have any thermal cutout problems. Hope this helps, Nick |
Another combi boiler hot water question
On 08/03/2019 12:24, AnthonyL wrote:
I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? When my oil fired combi went wrong I did think that with four multiple terminal relays it is to complicated for its own good. What I would quite like is a series of LEDs on the front panel that show the status of the relays, thermostats and other sensors. I was surprised to discover that it does not appear to care about the pressure in the central heating (and internal hot water tank) system. -- Michael Chare |
Another combi boiler hot water question
On Friday, 8 March 2019 12:24:34 UTC, AnthonyL wrote:
Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. It depends on combination of the boiler and the type of shower mixer. If the shower throttles back the flow of hot the temp rises and eventually the boiler will cut out. Some thermostatic mixers and some combis play nicely together, others fight. Owain |
Another combi boiler hot water question
On 08/03/2019 12:24, AnthonyL wrote:
I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I had that sort of problem from new with both a Vaillant and a Halstead, admittedly in an older and rambling house with longish pipe runs. Given up and gone to a proper system boiler. Some friends have a small holiday cottage that we use occasionally, this is a new compact house with very direct pipe runs and the shower is flawless, even with other demand on the small combi. |
Another combi boiler hot water question
On 08/03/2019 12:24, AnthonyL wrote:
I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I've seen this when the secondary plate exchanger was scaled up. Boiler would throttle the burner back, but when the plate exchanger gets so bad it can't conduct the minimum burner power through the lime scale, then the burner ends up cycling on and off. You might get a short improvement by turning the hot water temperature to max, as a higher temperature differential will enable more power to be passed through and it might be able to handle the full min burner power without cycling, but this will also scale up the plate exchanger faster, so it's only a very short term fix. I took the plate exchanger out and descaled it. It required an enormous amount of descaler - fortunately I had a 2kg tub of Furnox DS-3, and it took quite a while. A plumber would probably just replace the plate exchanger. -- Andrew |
Another combi boiler hot water question
On 08/03/2019 12:24, AnthonyL wrote:
I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On Friday, 8 March 2019 18:19:00 UTC, John Rumm wrote:
On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. the funny thing is these things are marketed as energy saving NT |
Another combi boiler hot water question
On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm
wrote: If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. Or --depending on your water-- descale the shower head... Thomas Prufer |
Another combi boiler hot water question
On Fri, 8 Mar 2019 13:06:28 +0000, Nick Odell
wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? Has it always done this? As a mere user of the Baxi 105HE, not an engineer thereof, I'm wondering where the CH & Hot Water temperature knobs are set? Mine are set so the temperature never quite goes up to 70 (I was told to do this to reduce limescale deposits though I don't know if that really works.) I never have any thermal cutout problems. I had some problem a few months ago that led me to deduce that having the knob set too low appeared to be causing cut out. I was set to about 2 'o' clock, I'm now on about 4 'o' clock. 6 'o' clock ie vertically down seems to be the max. I'll wind it back a notch or two and see what happens but I'm definitely hitting max temp at the current setting. -- AnthonyL |
Another combi boiler hot water question
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Another combi boiler hot water question
On Fri, 8 Mar 2019 16:22:03 +0000, newshound
wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I had that sort of problem from new with both a Vaillant and a Halstead, admittedly in an older and rambling house with longish pipe runs. Given up and gone to a proper system boiler. I thought the Vaillant was a proper system boiler? -- AnthonyL |
Another combi boiler hot water question
On Fri, 8 Mar 2019 16:30:09 +0000, Andrew Gabriel
wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I've seen this when the secondary plate exchanger was scaled up. Boiler would throttle the burner back, but when the plate exchanger gets so bad it can't conduct the minimum burner power through the lime scale, then the burner ends up cycling on and off. You might get a short improvement by turning the hot water temperature to max, as a higher temperature differential will enable more power to be passed through and it might be able to handle the full min burner power without cycling, but this will also scale up the plate exchanger faster, so it's only a very short term fix. I took the plate exchanger out and descaled it. It required an enormous amount of descaler - fortunately I had a 2kg tub of Furnox DS-3, and it took quite a while. A plumber would probably just replace the plate exchanger. Makes sense. Just a bit of a limit on what I should spend on a 2006 built boiler perhaps. Needed a new diverter valve 18 months ago. -- AnthonyL |
Another combi boiler hot water question
On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm
wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold. As stated the problem is when the burner goes out. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point. I'll give that a go. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No TMV afaia, simply turn anticlockwise to reduce the cold water. If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. Interesting, I'm wondering now when I did change the shower head because my wife found the other one too gentle. But that is probably the opposite to what you are proposing. -- AnthonyL |
Another combi boiler hot water question
On 09/03/2019 13:50, AnthonyL wrote:
On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold. As stated the problem is when the burner goes out. Yup, just including the description for completeness. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point. I'll give that a go. Alternatively you could try running the shower with just the hose (i.e. head removed) But note also the comment from Andy and others. A scaled shower head could cause a similar issue as could a scaled up secondary HX in the boiler. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No TMV afaia, simply turn anticlockwise to reduce the cold water. In which case you will need to be wary of setting the DHW top limit too high since you don't want to have a scalding risk. If you set it at 60 max, then by the time you allow for a bit of loss in the pipework etc that ought to be still cool enough to get out of the way should it start getting too hot. If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. Interesting, I'm wondering now when I did change the shower head because my wife found the other one too gentle. But that is probably the opposite to what you are proposing. Well a high flow rate head, with lots of wide jets may give a "softer" more rain like flow, that a lower consumption one with a smaller number of narrower more focussed jets. How hard the shower feels will be a product of the speed of the water and the weight of it hitting an area of the body. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On 09/03/2019 13:38, AnthonyL wrote:
On Fri, 8 Mar 2019 05:19:03 -0800 (PST), wrote: On Friday, 8 March 2019 12:24:34 UTC, AnthonyL wrote: Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. It depends on combination of the boiler and the type of shower mixer. If the shower throttles back the flow of hot the temp rises and eventually the boiler will cut out. Some thermostatic mixers and some combis play nicely together, others fight. I don't think it is a thermostatic mixer, simply turn and changes the ratio of hot/cold. That would be true of a thermostatic mixer as well though... Do you know what make/model of shower it is? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On 09/03/2019 13:39, AnthonyL wrote:
On Fri, 8 Mar 2019 16:22:03 +0000, newshound wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I had that sort of problem from new with both a Vaillant and a Halstead, admittedly in an older and rambling house with longish pipe runs. Given up and gone to a proper system boiler. I thought the Vaillant was a proper system boiler? Vaillant make Heating only boilers (vented and unvented), System boilers, and Combi boilers. Typically the 400, 600, and 800 series respectively. So a HE 624 is a 24kW System boiler and a 838 a 38 kW Combi. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On Sat, 9 Mar 2019 15:19:02 +0000, John Rumm
wrote: On 09/03/2019 13:39, AnthonyL wrote: On Fri, 8 Mar 2019 16:22:03 +0000, newshound wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? I had that sort of problem from new with both a Vaillant and a Halstead, admittedly in an older and rambling house with longish pipe runs. Given up and gone to a proper system boiler. I thought the Vaillant was a proper system boiler? Vaillant make Heating only boilers (vented and unvented), System boilers, and Combi boilers. Typically the 400, 600, and 800 series respectively. So a HE 624 is a 24kW System boiler and a 838 a 38 kW Combi. Goes to show what I know about boilers. Too many years with coal fired heating. I'm guessing our bungalow used to have a system boiler in the loft with supplementary immersion heating. In fact that's pretty well what I had in my previous coal fired property and to be honest that worked well as the immersion heater wouldn't need to do anything when there was a fire and kept a stock of hot water using E7 when heating was needed. -- AnthonyL |
Another combi boiler hot water question
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Another combi boiler hot water question
On 10/03/2019 10:40, AnthonyL wrote:
On Sat, 09 Mar 2019 13:50:19 GMT, lid (AnthonyL) wrote: On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum. Everything fine for a few minutes then the burner turns off, leds go back, and wife screams. Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out? Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar? Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold. As stated the problem is when the burner goes out. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point. I'll give that a go. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No it didn't do the job. Also if I turned the temperature down the boiler started cycling a bit erratically and with bit of what sounds like valves or circuit breaker noises. If I turned the temperature up it was better but would still cut out. No TMV afaia, simply turn anticlockwise to reduce the cold water. It is a Mira 415. I suspect put in at the same time as the boiler so 2006? Ah, ok the 415 is not a traditional TMV but a pressure balanced valve instead. These are specially designed for use with combi's since a traditional TMV can have unexpected results. (i.e. if the temp falls, a normal TMV will compensate by increasing the flow of hot. On a combi that might actually lower the temp of the hot supply even more. A PB valve will keep the pressure on the inlets balanced, this tends to better reflect the effect of demands being made elsewhere in the house) If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. I'm fairly sure the problem is in the boiler somewhere. The shower has worked fine in the 3 1/2 years we've been here. The only changes have been: 1) Flow reducer valve put in a couple of years ago 2) Change shower head to one that doesn't have such a fine spray 3) Replacement diverter valve about 18 months ago It's definitely cycling when it shouldn't and as I understand it now the burner should simply adjust and not turn off/on though I presume that it correct operation for the CH? The main difference between CH operation and DHW is the addition of the secondary plate heat exchanger for the DHW. Since we have now eliminated a lack of adequate DHW demand as a cause, it points the finger of suspicion at the Plate HX, and lack of adequate rate of heat transfer. The MO would be the system fires, but the primary side runs hotter since you are getting less cooling effect from the PHX. Hard water area? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On 10/03/2019 13:57, John Rumm wrote:
On 10/03/2019 10:40, AnthonyL wrote: On Sat, 09 Mar 2019 13:50:19 GMT, lid (AnthonyL) wrote: On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum.Â* Everything fine for a few minutes then the burner turns off, leds go back, and wife screams.Â* Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out?Â* Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar?Â* Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold.Â* As stated the problem is when the burner goes out. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point.Â* I'll give that a go. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No it didn't do the job. Also if I turned the temperature down the boiler started cycling a bit erratically and with bit of what sounds like valves or circuit breaker noises.Â* If I turned the temperature up it was better but would still cut out. No TMV afaia, simply turn anticlockwise to reduce the cold water. It is a Mira 415.Â* I suspect put in at the same time as the boiler so 2006? Ah, ok the 415 is not a traditional TMV but a pressure balanced valve instead. These are specially designed for use with combi's since a traditional TMV can have unexpected results. (i.e. if the temp falls, a normal TMV will compensate by increasing the flow of hot. On a combi that might actually lower the temp of the hot supply even more. A PB valve will keep the pressure on the inlets balanced, this tends to better reflect the effect of demands being made elsewhere in the house) If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. I'm fairly sure the problem is in the boiler somewhere.Â* The shower has worked fine in the 3 1/2 years we've been here.Â* The only changes have been: 1) Flow reducer valve put in a couple of years ago 2) Change shower head to one that doesn't have such a fine spray 3) Replacement diverter valve about 18 months ago It's definitely cycling when it shouldn't and as I understand it now the burner should simply adjust and not turn off/on though I presume that it correct operation for the CH? The main difference between CH operation and DHW is the addition of the secondary plate heat exchanger for the DHW. Since we have now eliminated a lack of adequate DHW demand as a cause, it points the finger of suspicion at the Plate HX, and lack of adequate rate of heat transfer. The MO would be the system fires, but the primary side runs hotter since you are getting less cooling effect from the PHX. Diverter valve. DHW thermostat. -- Max Demian |
Another combi boiler hot water question
On 10/03/2019 14:59, Max Demian wrote:
On 10/03/2019 13:57, John Rumm wrote: On 10/03/2019 10:40, AnthonyL wrote: On Sat, 09 Mar 2019 13:50:19 GMT, lid (AnthonyL) wrote: On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum.Â* Everything fine for a few minutes then the burner turns off, leds go back, and wife screams.Â* Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out?Â* Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar?Â* Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold.Â* As stated the problem is when the burner goes out. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point.Â* I'll give that a go. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No it didn't do the job. Also if I turned the temperature down the boiler started cycling a bit erratically and with bit of what sounds like valves or circuit breaker noises.Â* If I turned the temperature up it was better but would still cut out. No TMV afaia, simply turn anticlockwise to reduce the cold water. It is a Mira 415.Â* I suspect put in at the same time as the boiler so 2006? Ah, ok the 415 is not a traditional TMV but a pressure balanced valve instead. These are specially designed for use with combi's since a traditional TMV can have unexpected results. (i.e. if the temp falls, a normal TMV will compensate by increasing the flow of hot. On a combi that might actually lower the temp of the hot supply even more. A PB valve will keep the pressure on the inlets balanced, this tends to better reflect the effect of demands being made elsewhere in the house) If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. I'm fairly sure the problem is in the boiler somewhere.Â* The shower has worked fine in the 3 1/2 years we've been here.Â* The only changes have been: 1) Flow reducer valve put in a couple of years ago 2) Change shower head to one that doesn't have such a fine spray 3) Replacement diverter valve about 18 months ago It's definitely cycling when it shouldn't and as I understand it now the burner should simply adjust and not turn off/on though I presume that it correct operation for the CH? The main difference between CH operation and DHW is the addition of the secondary plate heat exchanger for the DHW. Since we have now eliminated a lack of adequate DHW demand as a cause, it points the finger of suspicion at the Plate HX, and lack of adequate rate of heat transfer. The MO would be the system fires, but the primary side runs hotter since you are getting less cooling effect from the PHX. Diverter valve. Not sure about that - all it can do is fail to divert (either at all, or completely), that would leave the rads still partly in circuit. That will increase the heating load rather than reduce it. DHW thermostat. Possibly - although I would expect it to shut off faster and also produce water not actually hot enough in the first place if it were over reading. Could be worth disconnecting it from the PCB, and measuring its resistance though. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On Sun, 10 Mar 2019 18:28:37 +0000, John Rumm
wrote: On 10/03/2019 14:59, Max Demian wrote: On 10/03/2019 13:57, John Rumm wrote: On 10/03/2019 10:40, AnthonyL wrote: On Sat, 09 Mar 2019 13:50:19 GMT, lid (AnthonyL) wrote: On Fri, 8 Mar 2019 18:18:50 +0000, John Rumm wrote: On 08/03/2019 12:24, AnthonyL wrote: I've been trying to understand what happens with the hot water when my wife screams that it has gone cold in the shower so I watched it the other day. Turn shower on, burner comes on, led lights (Baxi 105HE) start to light up to a maximum.Â* Everything fine for a few minutes then the burner turns off, leds go back, and wife screams.Â* Burner comes back on - repeat and rinse. Shouldn't the burner flame just adjust to maintain the temperature rather than cut-out?Â* Obvious behaviour of the CH but not for DHW. Otherwise is this indicative of a thermistor problem with hysterisis or similar?Â* Is it easy to replace? If we assume for the moment that the boiler is working as it should then there is a likely cause that could result from the boiler DHW temperature going over the set point. It's working as well as I can tell for the CH. IIUC, your Baxi does not have any form of flow regulation. So all it can do in response to varying DHW flow rates is modulate its burner output. So normally you set a temperature, say 60 deg, and the boiler will attempt to deliver water at that temp. If you are drawing DHW at a high rate, then its unlikely to have the power to reach that temp - and so the temp will fall below the max. That I'd be happy with as even though the water will not get very hot it is simply a matter of turning the shower knob anticlockwise to reduce the amount of cold.Â* As stated the problem is when the burner goes out. If however draw at a low rate, then it will have to modulate its burner output power down to prevent the temperature exceeding the limit. If it can't keep under the limit even at minimum burner power, then it will start to cycle the burner. That's what seems to be happening. You can test this theory, but running the shower as normal, but by adding some extra demand - say running the hot tap in the basin to increase the DHW flow rate a bit. Good point.Â* I'll give that a go. If that stops the burner cycling, then you may be able to fix the problem simply by increasing the max DHW temp on the boiler (the TMV on the shower should keep the person in there safe). No it didn't do the job. Also if I turned the temperature down the boiler started cycling a bit erratically and with bit of what sounds like valves or circuit breaker noises.Â* If I turned the temperature up it was better but would still cut out. No TMV afaia, simply turn anticlockwise to reduce the cold water. It is a Mira 415.Â* I suspect put in at the same time as the boiler so 2006? Ah, ok the 415 is not a traditional TMV but a pressure balanced valve instead. These are specially designed for use with combi's since a traditional TMV can have unexpected results. (i.e. if the temp falls, a normal TMV will compensate by increasing the flow of hot. On a combi that might actually lower the temp of the hot supply even more. A PB valve will keep the pressure on the inlets balanced, this tends to better reflect the effect of demands being made elsewhere in the house) If that still does not do it, then you may need to change the shower head for a more "thirsty" one, or use the basin tap trick for every shower. I'm fairly sure the problem is in the boiler somewhere.Â* The shower has worked fine in the 3 1/2 years we've been here.Â* The only changes have been: 1) Flow reducer valve put in a couple of years ago 2) Change shower head to one that doesn't have such a fine spray 3) Replacement diverter valve about 18 months ago It's definitely cycling when it shouldn't and as I understand it now the burner should simply adjust and not turn off/on though I presume that it correct operation for the CH? The main difference between CH operation and DHW is the addition of the secondary plate heat exchanger for the DHW. Since we have now eliminated a lack of adequate DHW demand as a cause, it points the finger of suspicion at the Plate HX, and lack of adequate rate of heat transfer. The MO would be the system fires, but the primary side runs hotter since you are getting less cooling effect from the PHX. Diverter valve. Not sure about that - all it can do is fail to divert (either at all, or completely), that would leave the rads still partly in circuit. That will increase the heating load rather than reduce it. New one put in 2017 though a lot of problem initially with cutting out due to a microswitch lever setting. I've not checked whether the nearby radiator gets warm when the CH is off. DHW thermostat. Possibly - although I would expect it to shut off faster and also produce water not actually hot enough in the first place if it were over reading. Could be worth disconnecting it from the PCB, and measuring its resistance though. I've taken some smartphone video of the panel whilst doing some tests. However I wasn't smart enough to use a smaller resolution that the max I can readily upload to video.com and I'm sure no-one really want 2Gb of LEDs going on/off. I'll post again once done. Meanwhile I note that when I run the hot water into a basin it looks creamy which then settles and I'm assuming it is just very small air bubbles. The Severn Trent website describes the water in the area as "Moderately hard". It gives a full list of chemical etc found in the water, but not Calcium (I thought that's what I'd be looking for. There's no major issue with kettle furring. Not too happy about Arsenic, Benzine and e-coli but I doubt that boiler minds. -- AnthonyL |
Another combi boiler hot water question
On 11/03/2019 13:03, AnthonyL wrote:
I can readily upload to video.com and I'm sure no-one really want 2Gb of LEDs going on/off. I am sure handbrake could edit that down a bit. -- In a Time of Universal Deceit, Telling the Truth Is a Revolutionary Act. - George Orwell |
Another combi boiler hot water question
On 11/03/2019 13:03, AnthonyL wrote:
On Sun, 10 Mar 2019 18:28:37 +0000, John Rumm wrote: On 10/03/2019 14:59, Max Demian wrote: Diverter valve. Not sure about that - all it can do is fail to divert (either at all, or completely), that would leave the rads still partly in circuit. That will increase the heating load rather than reduce it. New one put in 2017 though a lot of problem initially with cutting out due to a microswitch lever setting. I've not checked whether the nearby radiator gets warm when the CH is off. DHW thermostat. Possibly - although I would expect it to shut off faster and also produce water not actually hot enough in the first place if it were over reading. Could be worth disconnecting it from the PCB, and measuring its resistance though. I've taken some smartphone video of the panel whilst doing some tests. However I wasn't smart enough to use a smaller resolution that the max I can readily upload to video.com and I'm sure no-one really want 2Gb of LEDs going on/off. As TNP suggested, Handbrake could squish that into something far smaller if you want. I'll post again once done. Meanwhile I note that when I run the hot water into a basin it looks creamy which then settles and I'm assuming it is just very small air bubbles. Yup, not uncommon... The Severn Trent website describes the water in the area as "Moderately hard". It gives a full list of chemical etc found in the water, but not Calcium (I thought that's what I'd be looking for. They may give a figure for overall hardness in degrees Clarke? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Another combi boiler hot water question
On Mon, 11 Mar 2019 17:06:03 +0000, John Rumm
wrote: On 11/03/2019 13:03, AnthonyL wrote: On Sun, 10 Mar 2019 18:28:37 +0000, John Rumm wrote: On 10/03/2019 14:59, Max Demian wrote: Diverter valve. Not sure about that - all it can do is fail to divert (either at all, or completely), that would leave the rads still partly in circuit. That will increase the heating load rather than reduce it. New one put in 2017 though a lot of problem initially with cutting out due to a microswitch lever setting. I've not checked whether the nearby radiator gets warm when the CH is off. DHW thermostat. Possibly - although I would expect it to shut off faster and also produce water not actually hot enough in the first place if it were over reading. Could be worth disconnecting it from the PCB, and measuring its resistance though. I've taken some smartphone video of the panel whilst doing some tests. However I wasn't smart enough to use a smaller resolution that the max I can readily upload to video.com and I'm sure no-one really want 2Gb of LEDs going on/off. As TNP suggested, Handbrake could squish that into something far smaller if you want. My Handbrake installation (requiring also an install of Framework) failed but I've also had a flakey connection for a day or so. Anyway copy/pasting a FFMPEG command into my Linux terminal worked without needing any addition software and has seriously reduced the file sizes. I'll post again once done. There are three videos, sorry a bit like watching paint dry, with narrative included to say what I'm doing: https://vimeo.com/323440152 https://vimeo.com/323440503 https://vimeo.com/323441923 I've left the temperature setting at minimum and my wife has just had a shower, needed the Mira turned right up to max which we've never had before and it was just hot enough for her and no cut outs. So that, plus possibly what is to be seen in the videos, indicates that something is overheating. Meanwhile I note that when I run the hot water into a basin it looks creamy which then settles and I'm assuming it is just very small air bubbles. Yup, not uncommon... Noted The Severn Trent website describes the water in the area as "Moderately hard". It gives a full list of chemical etc found in the water, but not Calcium (I thought that's what I'd be looking for. They may give a figure for overall hardness in degrees Clarke? Analysis Typical Value Hardness Level Moderately Hard Hardness Clark 13.53 That was for the year to last September. -- AnthonyL |
Another combi boiler hot water question
|
Another combi boiler hot water question
On 14/03/2019 08:17, Thomas Prufer wrote:
On Wed, 13 Mar 2019 13:07:50 GMT, lid (AnthonyL) wrote: Analysis Typical Value Hardness Level Moderately Hard Hardness Clark 13.53 Maybe the heat exchanger between hot water and combi water is furred up. Low flow, combi can't dump heat to the DHW fast enough. And local hot spots in the heat exchanger cause more scale to precipitate, starting a vicious circle. It's possible to descale them by pumping a suitable acid through the combi, heat exchanger in situ... Rothenberger, for instance, make units with an acid tank, reversible pump, hoses, and bells and whistles. Nothing you can't jury-rig with a "drill pump"... I've done one. I took it out and did it in a washing up bowl. It used a lot of descaler (Furnox DS-3). There was also a lot of rust debris caught in the primary side, which came out during the descaling. -- Andrew Gabriel |
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