Combi Boiler temperature dials

[ldoodle]

What's the 'best' temperature to set the temperature dials to, on the boiler itself?

British Gas say this:

If your boiler has two dials set the heating control at a high setting (80°C).

We had our boiler installed last year and one thing I found during the winter is that the room stat will bring it up to temp so the boiler will then shut off. 10 minutes later the temp will drop as boiler is off so it would fire up again.

Rinse and repeat. Can't be efficient to continuously fire on and off.

Ours does have separate dials for water and heating; the heating dial is currently set to about 45. We have TRVs on all rads.

Thanks

 

[Dan Robinson]

And the boiler is?

 

[ldoodle]

Sorry! Ideal Logic+ 35kw.

 

[Dan Robinson]

Set the hot water to wherever you want it.

Heating should be as low as will work.

If the room stat si cycling the boiler every ten minutes then it is installed incorrectly.

If the boiler is cycling every ten minutes then it is probably fine. We set most of our boiler to around 60 - 65 for the heating.

 

[ldoodle]

How would I know if it's the boiler cycling or the room stat cycling? It's still happening.

The stat is the Honeywell CMT927. I can see it firing up the boiler (the little flame icon comes on), then when the Room temp reaches the Target temp, the flame icon goes out, turning the boiler off.

I would have thought it would be better to just maintain the target temp instead of just running straight past it and continuously increasing and dropping the temp and firing on/off.

Thanks

 

[Dan Robinson]

Cm927 has TPi controls so the cycling depends how close it is to target temperature.

Ignore the flame symbol, it means little in practice.

The green light on the receiver tells you when the stat is calling for heat from the boiler.

The boiler then sorts itself out.

Problem with TPi, if that it conflicts with the boilers own modulation protocol.

It was great on the old SE boilers, less effective on today's breed. Still better than nothing.

 

[D_Hailsham]

The flame icon on a 927 is not a reliable indicator. (It's showing on mine yet the room and target temperatures are identical and the boiler is not running.)
Check what the green light on the receiver is showing. If this is on but the boiler is off then the boiler stat has turned it off.

Your boiler needs 35kW to provide instant hot water but the CH requirement will be much less, possible only 10kW when it's very cold. (Use Whole House Boiler Size Calculator to find out how much.) and much less when it's mild. The CH output of your boiler is 7kW to 24kW, so when it's mild and less than 7kW is required the boiler will cycle, even if the room stat is calling for heat.

 

[D_Hailsham]

Just re-read your first post. You say you have TRVs on all rads. Is that correct? If so, the TRV on the rad where the CM927 is located must be set to Max.

 

[ldoodle]

As long as it's not "wrong" it's fine. Though I've seen there's a Cycle Rate option on the CM927 (not CMT927, sorry). It's set to 6 per hour (default).

Just re-read your first post. You say you have TRVs on all rads. Is that correct? If so, the TRV on the rad where the CM927 is located must be set to Max.

We have the stat on the stand and sometimes (rarely) take it with us to bed. It's normally in the open plan lounge/dining room, on a shelf right between 2 rads. Do they both need to be on MAX?

Thanks again everyone.

 

[Dan Robinson]

Try changing the cycle rate to 3 and minimum on time to 5.


Don't move it around,, it screws with the fuzzy logic (assuming it is turned on).

If you do me it, it needs four or so days to settle down again.

 

[D_Hailsham]

Ideally both rad TRVs should be set to max (and so should the bedroom TRV when you take the controller upstairs). If you don't do this and the TRV is set to a lower temperature than the controller, the room will never get up to the temperature set on the controller. So the boiler will run and run and run - until the boiler stat takes over.