Honeywell CM67 with Potterton Gold 24 combi boiler

[londonben]

I've just had a Potterton Gold 24 boiler fitted, and I've purchased a Honeywell CM67 wireless thermostat to use with it.
The fitter has said he can't use it as the Gold 24 has a built in clock and this thermostat is a controller not just a thermostat.
He says he has phoned Potterton and they have said the same to him.

I find this a little strange, because as I see it (and I'm probably wrong) the thermostat sends a signal to fire the boiler to heat the radiators, so if the clock on the boiler was set to 'on' and not timed, it would only fire when signalled by the thermostat, which in turn would only send the signal when timed to do so.

In the install guide for the boiler it says "If the thermostat has an anticipator it must be wired as fig 29" Is the anticipator the same as optimizer or something else.

Sorry if this is clear as mud

 

[ArtfulBodger]

Your installer is talking absolute nonsense. The CM67 is a programmable room thermostat that does not have an anticipator. If it did, it would require a 230V mains supply, which it doesn't.

What thermostat has he wired up to it then?

 

[londonben]

ArtfulBodger, I'm not sure what he's done yet. He's fitting today/tomorrow and I'm still at work so haven't got home to see the mess.
The honeyweel CM67 Rf receiver does require a 230v supply I beleive, so that maybe the problem.

I hadn't really thought about why it might need a 230v supply.

 

[ArtfulBodger]

Oops, missed the RF bit! doesn't matter though, the receiver although plugged into the mains is still just a voltage free relay.

The clock should be bypassed via the continuous run switch and the whole lot should be controlled by the CM67 - which is a very good box BTW.

Completely, utterly, bog standard.

 

[londonben]

ArtfulBodger, thanks. So the 230V is to power the wireless reciver, and it just acts like an ordinary room stat.

What is an anticipator?. As it says in the boiler instal instructions it must be wired as of fig29. This would seem to be very specefic, as it looks like the wiring for an ordinary room stat is a bit more flexible.

 

[ArtfulBodger]

An anticipator is a tiny heater within the room thermostat that is supposed to make the operation of the stat a lot more accurate. Dunno anything more about them than that, loads of others here know more than me.'

If you actually look at the boiler where you make the roomstat connection you will see a single bit of wire forming a bridge across 2 terminals. Obviously it is completing a circuit and forces the boilers heating operation to be controlled only be the clock and its own internal thermostat. This leads to the boiler cycling up and down continuously, wasting a lot of money.

This bridge is replaced by the 2 wires coming from the room thermostat. The purpose of the volt free relay is to complete the same circuit when there is a demand for central heating. It is that simple. The boiler is now controlled by the room thermostat (and the internal stat), leading to a decrease in heating bills.

 

[Agile]

As part of the mass production era its cheaper to produce a simple thermostat which say switches off at 23*C and back on again at say20*C.

Thats too wide a gap for heating use, so a small resistor of about 120K is fitted across the mains supply so when the stat is "on". This heats up the stat and makes it switch off early.

The effect of this is to make the effective control range of a cheap stat say one degree instead of three!

Thats the real reason! But it does not sound very good to publicise! To be honest it does have an anticipatory effect as well which is what IS publicised. "The heat anticipator heats the stat and causes it to switch off before the room has reached the target because the hot rads will continue to give out heat for a while after the source is switched off".

Tony

 

[londonben]

If you actually look at the boiler where you make the roomstat connection you will see a single bit of wire forming a bridge across 2 terminals. Obviously it is completing a circuit and forces the boilers heating operation to be controlled only be the clock and its own internal thermostat. This leads to the boiler cycling up and down continuously, wasting a lot of money.

This bridge is replaced by the 2 wires coming from the room thermostat. The purpose of the volt free relay is to complete the same circuit when there is a demand for central heating. It is that simple. The boiler is now controlled by the room thermostat (and the internal stat), leading to a decrease in heating bills.

ArtfulBodger, I'm home now and have looked trough the install instructions for both thermostat and boiler. I thought I had it pegged in my head but your phrase "volt free relay" has me slightly confused as the boiler instructions say:

Remove the link between 1 & 2 The 230V supply at terminal 1 can be connected to the thermostat. The switched output from the thermostat must be connected to terminal 2.
The diagram shows the dotted connection through thermostat from terminals 1 & 2 and this shows the 230V from terminal 1.

I feel a bit dumb, but this doesn't sound volt free.

 

[Gasman1015]

You can still use the the CM67 for volt free or 230volt.