Vaillant EcoTec+ 837 with Honeywell CM907 - cycling on/off

[plumbamateur]

Hi, just wondered if anyone is able to offer a word of advice. I have the above boiler and thermostat combination, relatively new (<1 year) - and have noticed that sometimes the thermostat starts the boiler (as the room temp falls), only to stop it again a minute or 2 later.

The CM907 makes an audible click (a relay, I guess) when switching on/off, so it's quite easy to hear what's happening.

I had presumed that either the boiler or the stat would have some sort of mechanism to stop this cycling, as it can't be very efficient. Would I be better off with a Vaillant thermostat or something, which is designed for my boiler??

Any ideas gratefully received - thanks

 

[plumbamateur]

Any thoughts, anyone?

 

[jpm777]

Hi,
I'm by no means an expert but have a Honeywell thermostat also and that is the component that is making all your cycling happen. They are very sensitive, however they are meant to be efficient, particularly if set up correctly. They maintain a very stable temperature, but cycle the boiler a lot to achieve this.

 

[jpm777]

Hi,
I'm by no means an expert but have a Honeywell thermostat also and that is the component that is making all your cycling happen. They are very sensitive, however they are meant to be efficient, particularly if set up correctly. They maintain a very stable temperature, but cycle the boiler a lot to achieve this.

 

[jpm777]

Hi,
I'm by no means an expert but have a Honeywell thermostat also and that is the component that is making all your cycling happen. They are very sensitive, however they are meant to be efficient, particularly if set up correctly. They maintain a very stable temperature, but cycle the boiler a lot to achieve this.

 

[Agile]

That cycling problem is very likely if the stat is placed too close to a radiator!

If thats the case try reducing the flow through the rad using the lockshield valve.

I think that its also possible on that stat to set the hysteresis to 0.5 C or to 1.0 C. The 1.0 C setting would reduce the cycling.

Tony

 

[David937]

It's the Chronotherm technology on the thermostat, ours was well away from any radiators and it still done this, it does maintain a very steady temperature but I don't really know how efficient it is.

Tried adjusting the proportional band width, cycle rate and just about every other setting but still wasn't really pleased with it.

We replaced ours with a Vaillant controller.

 

[plumbamateur]

Just logged in and saw the replies, thanks very much all.

Agile - I'll try the adjustment first- ta

The stat is in the hall and probably a good 4m away from the nearest rad

Thanks again

 

[Agile]

The boiler does have a ( setable ) anti cycling delay of about 5 minutes so it will not come on again until after that time since it last fired.

Its also possible your boiler power output is set way too high. Search on range rating.

In your case it seem the stat is responding too quickly to heat from the nearby rad. Try watching the displayed temp as the boiler starts up.

Just because the stat is demanding heat it does not mean the boiler has necessarily fired up.

Tony

 

[plumbamateur]

Thanks Tony, i'll try watching the stat when the heating comes on.

I do indeed have the temperature set quite high on the boiler, I'd say it's set to about 90% of the maximum. Is this considered too high? I set it to this as the radiators didn't feel enormously hot...

David