Hi all,
There is no stat on my hot water cylinder. Result is almost boling water coming out the hot taps which is both dangerous and expensive.
I would fit one and run the cable but there is no wiring centre, all the wiring from boiler, pump, room stat run into back of programmer (potterton Ep200).

There's no evidence of any 2 or 3 port valves so I can't work out how the system works i.e CH and HW independent or together as required.

Can I still fit one? If so how and is there anything else I should check out first?

In an earlier contribution to this discussion,
Charlie Pie wrote:

Hi all,
There is no stat on my hot water cylinder. Result is almost boling
water coming out the hot taps which is both dangerous and expensive.
I would fit one and run the cable but there is no wiring centre, all
the wiring from boiler, pump, room stat run into back of programmer
(potterton Ep200).

There's no evidence of any 2 or 3 port valves so I can't work out how
the system works i.e CH and HW independent or together as required.

Can I still fit one? If so how and is there anything else I should
check out first?

I would guess that you have two virtually independent pairs of pipes
connected to your boiler (although they may possibly combine close to the
boiler so as to have only two physical connections to it).

One pair will be 28mm pipes connected to the coil in the hot water cylinder,
and water in this circuit will circulate by "gravity" (natural convection).
The other pair (probably 22mm pipes) will be for the central heating - and
will use a pump to pump the water round to the radiators.

In the absense of any control valves, whenever the heating is on water will
continue to circulate round the HW circuit and will raise the temperature of
the stored hot water to almost that of the boiler output.

The cure for this problem is either to convert the system to a fully pumped
setup with two zone valves or a single 3-port valve (S-Plan or Y-Plan), OR
to convert it to a C-Plan system. A C-plan requires the least changes -
simply requiring a cylinder stat, and a zone valve in the HW circuit. This
will have the effect of stopping the hot water getting too hot, and of
shutting down the boiler when both HW and CH are up to temperature. For
details of all these options, have a look at
http://content.honeywell.com/uk/homes/systems.htm

--
Cheers,
Set Square
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In message , Set Square
writes
In an earlier contribution to this discussion,
Charlie Pie wrote:

Hi all,
There is no stat on my hot water cylinder. Result is almost boling
water coming out the hot taps which is both dangerous and expensive.
I would fit one and run the cable but there is no wiring centre, all
the wiring from boiler, pump, room stat run into back of programmer
(potterton Ep200).

There's no evidence of any 2 or 3 port valves so I can't work out how
the system works i.e CH and HW independent or together as required.

Can I still fit one? If so how and is there anything else I should
check out first?

I would guess that you have two virtually independent pairs of pipes
connected to your boiler (although they may possibly combine close to the
boiler so as to have only two physical connections to it).

One pair will be 28mm pipes connected to the coil in the hot water cylinder,
and water in this circuit will circulate by "gravity" (natural convection).

These pipes may also be 22mm , mine were.


--
Chris French, Leeds

The cure for this problem is either to convert the system to a fully
pumped
setup with two zone valves or a single 3-port valve (S-Plan or Y-Plan), OR
to convert it to a C-Plan system.

Another solution if the boiler is the type that can't support valving on the
gravity circuit (only solid fuel or really old boilers might be like this),
is to:

(a) Put a cylinder thermostat inline with the HW On output from the
programmer. This will limit temperature and improve fuel efficiency when on
HW only mode. When the CH is actually on, it will still overheat, though.

(b) To solve that problem, stick a TMV (thermostatic mixing valve) on the
output. This will mix the very hot water with cold, to bring it down to a
safe temperature (i.e. 55C). You may need to add a pump to get good shower
performance.

Obviously, a better solution would be to replace the boiler in this sort of
situation. If you have a boiler that can support valving, or, better still,
capping off the gravity circuit, then go with Set Square's suggestion.

Christian.

Charlie Pie wrote in message ...
Hi all,
There is no stat on my hot water cylinder. Result is almost boling
water coming out the hot taps which is both dangerous and expensive.
I would fit one and run the cable but there is no wiring centre, all
the wiring from boiler, pump, room stat run into back of programmer
(potterton Ep200).

There's no evidence of any 2 or 3 port valves so I can't work out how
the system works i.e CH and HW independent or together as required.

Can I still fit one? If so how and is there anything else I should
check out first?

Wot Mr S Square said. I'm familiar with the Potterton EP2000
programmer and this has enough terminals inside to act as a wiring
centre for most standard central heating wiring arangements, or at
least with only the addition of a choc block 2 way connector.

--
Malc

Thanks all for advice so far.
As suggested both HW and CH are independent and connected to the boiler (potterton neteheat 16-22 Mk2 F) with 28mm pipes.
The boiler supports valving according to tech help at Potterton so the easiest option till I replace the boiler is to fit a 2 port to the HW system.
Please excuse the dimwit questions but is this a major job, and capping off the gravity circuit means what exactly?

The boiler supports valving according to tech help at Potterton so the
easiest option till I replace the boiler is to fit a 2 port to the HW
system.

You might want to stick a pump on there too. You may need a relay or two so
that you can run the pumps independently. Alternatively, don't use a 2 port
valve at all, just use a pump, an antigravity valve and a relay for boiler
interlock.

Please excuse the dimwit questions but is this a major job, and capping
off the gravity circuit means what exactly?

An alternative is to cap off the gravity circuit and run the hot water
cylinder from the pumped central heating side with modern format controls.
The gravity circuit is usually then used solely as the vent and water feed,
with any actual heating appliance connections capped off. The advantage of
doing this is that it simplifies the installation of a new boiler in the
future, as the pipework layout and heating controls are to modern standards.

When making modifications to old boilers, you must consider the vent/feed
paths. The vent path must be unvalved all the way to the exit. Unless your
boiler has a secondary lockout, it must also not be possible to block the
feed path to the boiler. The feed and vent may not share pipework, as the
escaping gas in the vent will block the ingress of quenching water. These
requirements don't apply to boilers that have an overheat cutout, as such
boilers don't rely on the quenching effect of new water introduced into the
system.

Christian.




"Charlie Pie" wrote in message
...

Christian McArdle Wrote:
The cure for this problem is either to convert the system to a fully
pumped-
setup with two zone valves or a single 3-port valve (S-Plan or
Y-Plan), OR
to convert it to a C-Plan system.-

Another solution if the boiler is the type that can't support valving
on the
gravity circuit (only solid fuel or really old boilers might be like
this),
is to:

(a) Put a cylinder thermostat inline with the HW On output from the
programmer. This will limit temperature and improve fuel efficiency
when on
HW only mode. When the CH is actually on, it will still overheat,
though.

(b) To solve that problem, stick a TMV (thermostatic mixing valve) on
the
output. This will mix the very hot water with cold, to bring it down to
a
safe temperature (i.e. 55C). You may need to add a pump to get good
shower
performance.

Obviously, a better solution would be to replace the boiler in this
sort of
situation. If you have a boiler that can support valving, or, better
still,
capping off the gravity circuit, then go with Set Square's suggestion.

Christian.

Thanks all for advice so far.
As suggested both HW and CH are independent and connected to the boiler
(potterton neteheat 16-22 Mk2 F) with 28mm pipes.
The boiler supports valving according to tech help at Potterton so the
easiest option till I replace the boiler is to fit a 2 port to the HW
system.
Please excuse the dimwit questions but is this a major job, and capping
off the gravity circuit means what exactly?


--
Charlie Pie

In an earlier contribution to this discussion,
Charlie Pie wrote:


Thanks all for advice so far.
As suggested both HW and CH are independent and connected to the
boiler (potterton neteheat 16-22 Mk2 F) with 28mm pipes.
The boiler supports valving according to tech help at Potterton so the
easiest option till I replace the boiler is to fit a 2 port to the HW
system.
Please excuse the dimwit questions but is this a major job, and
capping off the gravity circuit means what exactly?

It's not a *major* job, but there are a few things you need to bear in mind.
Firstly, there must be a clear - unvalved - path from the boiler to the
point where the fill and expansion pipes are connected. This usually means
that the 2-port valve needs to go very close to the HW cylinder, after these
connections. If the expansion pipe is connected too close to the cylinder to
allow this, you will need to re-jig the pipework a bit - and move the
expansion pipe connection a bit further away.

The valve must have a set of volt-free contacts which close when the valve
is open, and it must be wired up *exactly* as shown in the C-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm in order to ensure that
the boiler only runs when either the HW or CH (or both) are demanding heat,
and that the HW circuit is closed off once the HW demand is satisfied.

You will, of course, need to partially drain the system in order to fit the
valve - and then re-fill and bleed it - and top up the inhibitor -
afterwards.

I'm not quite sure what Christian was referring to by "capping off" the
gravity circuit. I think he probably meant that if you converted it to a
fully pumped Y-plan ot S-plan system, the CH and HW would largely share one
pair of pipes, so you could blank off the other pair.
--
Cheers,
Set Square
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Thanks again, one final question. Have had a look at the schematic at the above web site, the valve is shown on the return and from your info I'm assuming it should be on the flow side after the vent connection?
Cheers.

In an earlier contribution to this discussion,
Charlie Pie wrote:


Thanks again, one final question. Have had a look at the schematic at
the above web site, the valve is shown on the return and from your
info I'm assuming it should be on the flow side after the vent
connection? Cheers.

No, the return side is fine if that's easier and - I think - provided the
boiler has an overheat trip. See Christian's post for a bit more detail on
this. The absolute rule is that the valve *mustn't* be between the boiler
outlet and the vent pipe.
--
Cheers,
Set Square
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In an earlier contribution to this discussion,
Charlie Pie wrote:


Actually the return side is impossible to get at, so the flow side is
ok?

Yes, subject to not blocking the boiler's vent path.
--
Cheers,
Set Square
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On Wed, 13 Oct 2004 21:41:58 +0100, Charlie Pie
wrote:


Hi all,
There is no stat on my hot water cylinder. Result is almost boling
water coming out the hot taps which is both dangerous and expensive.
I would fit one and run the cable but there is no wiring centre, all
the wiring from boiler, pump, room stat run into back of programmer
(potterton Ep200).

There's no evidence of any 2 or 3 port valves so I can't work out how
the system works i.e CH and HW independent or together as required.

Can I still fit one? If so how and is there anything else I should
check out first?

Almost certainly the system is a so-called "gravity" type, where the
cylinder is heated by the convection of water from the boiler to
cylinder coil. The clues are normally that there are four pipes from
the boiler - two 22mm for heating are typical and two 28mm for the
cylinder. Basically then, the boiler turns on and off with its
internal thermostat and the water in the cylinder will be limited in
temperature only by that and the timer. The CH works simply by
having the room thermostat operate the pump.

Normally in these systems you can have HW only or CH and HW but not CH
without HW.

There are four main solutions:

1) A Honeywell C Plan arrangement. This uses a zone valve on the HW
part of the circuit controlled by a cylinder thermostat. You would
need to put in a wiring centre of some sort and wire the controls and
timer to do the job. From the plumbing perspective it is easy, but
you need to take care on siting the valve and not put it between the
boiler and vent or feed pipes to the loft header tank.

2) A Honeywell W plan where the system uses a diverter valve and you
change operation to fully pumped. This is more plumbing, but the
advantage is that the HW will heat much more quickly.

3) A Honeywell Y plan which is a similar technique to W plan but will
give CH and HW simultaneously. Whether this is worth it is
debatable if you are pumping the system.

4) A Honeywell S plan where there are two zone valves.

Details of these at

http://content.honeywell.com/uk/homes/systems.htm

Another alternative, which is conceptually like C-plan is to use a
second pump on the HW circuit, plus either a zone valve or a flap
valve which opens when the pump runs. This may be easier to plumb
but may require a relay to do the switching because you don't have the
auxilliary contacts of a motorised valve if you have pump only.




--

..andy

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