I have a CH system with gravity-fed HW. The controller has two output
terminals, one (nominally the HW connection) connects to the boiler and
the other (nominally the CH connection) to the pump. The controller
arranges that when there is demand for CH it switches both outputs on.
I assume this is all pretty standard.

I've got a wireless room thermostat/controller (Towerstat RF) which I
want to use to control the CH. It only has one output (it has
connections for live, neutral, and output). It has two temperature
settings, for day and for night. So I'm thinking I will have to use it
alongside the existing controller so that I still have a timer for the
HW.

I can't work out how to wire everything together so that the new one
controls the CH and the old one the HW. If I wire the new one to the
pump and boiler, and the old one just to to the boiler for HW, then the
pump will come on with the HW as they'll effectively be wired together.
I thought that I could set the old one to be on permanantly for CH, and
take the output of that to the new controller. But then the boiler will
be on all the time. Basically I can't see a way of getting thermostat
controlled cental heating 24 hrs a day without the HW being on all the
time. I guess this wouldn't be so much of a problem if there was a
thermostat on the HW tank, but there isn't.

Can I achieve what I want with the kit I've got?

Steve

In an earlier contribution to this discussion,
Steve wrote:

I have a CH system with gravity-fed HW. The controller has two output
terminals, one (nominally the HW connection) connects to the boiler
and the other (nominally the CH connection) to the pump. The
controller arranges that when there is demand for CH it switches both
outputs on. I assume this is all pretty standard.

I've got a wireless room thermostat/controller (Towerstat RF) which I
want to use to control the CH. It only has one output (it has
connections for live, neutral, and output). It has two temperature
settings, for day and for night. So I'm thinking I will have to use it
alongside the existing controller so that I still have a timer for the
HW.

I can't work out how to wire everything together so that the new one
controls the CH and the old one the HW. If I wire the new one to the
pump and boiler, and the old one just to to the boiler for HW, then
the pump will come on with the HW as they'll effectively be wired
together. I thought that I could set the old one to be on permanantly
for CH, and take the output of that to the new controller. But then
the boiler will be on all the time. Basically I can't see a way of
getting thermostat controlled cental heating 24 hrs a day without the
HW being on all the time. I guess this wouldn't be so much of a
problem if there was a thermostat on the HW tank, but there isn't.

Can I achieve what I want with the kit I've got?

Steve

No - but your system is very wasteful of energy, and worthy of an upgrade,
anyway!

The simplest upgrade for a gravity HW/pumped CH system is to convert it to
C-Plan - for which you will need a motorised valve in the HW circuit, and a
cylinder stat. This gives you independent control over HW and CH and only
runs the boiler when one or other (or both) are calling for heat, and only
runs the pump when CH is calling for heat.

Have a look at C-Plan in http://content.honeywell.com/uk/homes/systems.htm

If you do this, you will have to remove the link in the existing programmer
which turns the HW on when CH is selected. If your room stat is a
programmable one - providing different temperatures at different times of
day - you can use *that* to time the CH. In that case you would use the
timer in the old programmer just for HW, and set CH to 'constant'.

Hope this makes sense!
--
Cheers,
Roger
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Roger Mills (aka Set Square) wrote:

If you do this, you will have to remove the link in the existing programmer
which turns the HW on when CH is selected. If your room stat is a
programmable one - providing different temperatures at different times of
day - you can use *that* to time the CH. In that case you would use the
timer in the old programmer just for HW, and set CH to 'constant'.

Yes, it is, and that's exactly what I was hoping to do with the system
as it is, until I realised that would mean the HW being on all the
time. I was hoping for just one improvement for now, with the upgrades
you've suggested some later. But if I can't do it that way, then so be
it.

Thanks,
Steve

Roger Mills (aka Set Square) wrote:

No - but your system is very wasteful of energy, and worthy of an upgrade,
anyway!

A thought occurred to me - could I not achieve what I want using a
double-pole relay to switch the CH (one pole for pump and one for
boiler)? This would avoid the problem, I think, of the pump coming on
when the HW only was on?

By the way, how do you fit a thermostat to a HW tank when it has
pre-applied insulation rather than a jacket? Do you have to scrape off
some of the insulation?

Steve

In an earlier contribution to this discussion,
Steve wrote:

Roger Mills (aka Set Square) wrote:

No - but your system is very wasteful of energy, and worthy of an
upgrade, anyway!

A thought occurred to me - could I not achieve what I want using a
double-pole relay to switch the CH (one pole for pump and one for
boiler)? This would avoid the problem, I think, of the pump coming on
when the HW only was on?

Yes, I was thinking along the same lines after reading your previous reply.
I don't think that the relay needs to be double pole - single will do. If
you wire the coil in parallel with the pump, you can switch the boiler on
whenever the pump is running - but can still have *just* the boiler when
HW-only is selected. that would give you a *degree* of independence - but
the HW would still get (potentially too) hot whenever the CH was on -
whether you wanted it or not, and there would still not be a boiler
interlock - so the boiler would continue to waste energy keeping itself hot
unnecessarily.

By the way, how do you fit a thermostat to a HW tank when it has
pre-applied insulation rather than a jacket? Do you have to scrape off
some of the insulation?

Just that. You cut out a chunk of insulation - 50mm x 30mm or whatever - so
that the stat makes contact with the copper cylinder.

--
Cheers,
Roger
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Roger Mills (aka Set Square) wrote:

I don't think that the relay needs to be double pole - single will do. If
you wire the coil in parallel with the pump, you can switch the boiler on
whenever the pump is running - but can still have *just* the boiler when
HW-only is selected.

Oh yes, very clever. I think I'll go for this simpler approach for now
to at least give me a thermostat on the CH, and go for a stat on the
tank and a valve when the weather's warmer and I can be without the CH
while I do it.

Just that. You cut out a chunk of insulation - 50mm x 30mm or whatever - so
that the stat makes contact with the copper cylinder.

Many thanks for all your help.

Steve