Thermostat recommendation.

[spikeywan]

Seeing as how I went to all the trouble of registering, I might as well ask this as well...

My boiler has a simple twice a day on-off timer, and the thermostat is a simple dial to set it to one temperature.

I'd like to replace the thermostat with a combined timer and thermostat unit, that will allow me to set a minimum temperature as well as a maximum, give me at least 2 'on' cycles a day, and preferably have a 2 week cycle, so I can set each day differently. 1 week would do if a 2 week one was too expensive. Oh, and of course it needs to not cost a narm an daleg.

Luckily the current thermostat is mains powered, so I don't need a battery powered one, but something that won't lose it's settings in a power cut would be good, too.

What would you recommend?

Thanks.

[doitmyself]

Honeywell CM907. Seven days, six time/temperature settings per day.

It's battery operated, but they last at least 2 years.

I don't know anyone who makes a two-week programmer.

[spikeywan]

That looks well cool, thanks!

I wonder how it calculates what time to turn the boiler on in optimum start mode?

Surely different houses and boilers take different lengths of time to get up to temperature.

[doitmyself]

I wonder how it calculates what time to turn the boiler on in optimum start mode?

Surely different houses and boilers take different lengths of time to get up to temperature.

Not sure of the exact method, but it has to "learn" what time to come on, which takes a few days. It presumably can store data on the rate at which the temperature drops overnight and use this to estimate when to come on. I have been running an experiment since September recording the actual switch on time. The maximum I have seen is two hours before the required time during the recent cold weather and the shortest has been 7 minutes!

[spikeywan]

I asked Honeywell, and you're right, it does learn. It starts by assuming that there's a heat ramp of 3 degrees per hour, but it learns the real rate over a few days. This is a well cool feature. It's worth changing just for this!

I found it on-line at £61.25 plus shipping, and MeLocal City Plumbing will do me one for £61.50. Result!

I'm pretty sure how to wire it up, but just to check...

My existing thermostat has 4 wires. 3 mains, and a yellow wire which looks like it gets connected to the live to turn the boiler on.

They honeywell CM907 says "Two wire, volt free connections are ideal for use with combination boilers."

So I take it that with this new one, all I need to do is connect the live and the yellow switched live to it?

Hopefully it'll have some unused terminals I can put the neutral and earth into.

[doitmyself]

My existing thermostat has 4 wires. 3 mains, and a yellow wire which looks like it gets connected to the live to turn the boiler on.

So I take it that with this new one, all I need to do is connect the live and the yellow switched live to it?

Yes the live goes to A and the switched live to B

Hopefully it'll have some unused terminals I can put the neutral and earth into.

Do not try using terminal C; it will fry the stat. If you can find the other ends, disconnect them and cut back to the outer sheath at both ends. Or else connect them, separately, into a terminal block which can hide in the wall behind the stat.

[spikeywan]

Good job I checked!

[spikeywan]

If you can find the other ends, disconnect them and cut back to the outer sheath at both ends.

Hopefully the other ends should be easy enough to track down at the boiler end. I won't be removing them, though, and I'll be keeping the old thermostat to put back on if I move.

Cos if I move the CM907 will be going with me!!

[doitmyself]

Hopefully the other ends should be easy enough to track down at the boiler end. I won't be removing them, though, and I'll be keeping the old thermostat to put back on if I move.

Then just put the spare wires into a terminal block at the stat end.

if I move the CM907 will be going with me!!

You will have to change back before the agents/prospective buyers come round!