Does my central heating cycle on and off too quickly?

[Old_Badger]

After my central heating settles down it cycles on and off and on again every 9 minutes or so. Is this normal or is it much too frequent? Will it shorten the life of my boiler?

 

[chrishutt]

My crystal ball shows me a star, ..... a green looking star .....could that be something to do with your boiler?

 

[bengasman]

Is that 9 minutes between on and on or between off and on?

 

[JohnD]

you have got a room stat, haven't you?

 

[Old_Badger]

It's about 9 minutes between on and on. My boiler turns on for about 4 minutes followed by off for about 5 minutes.

I have a Danfoss room stat in the hall and this is what is controlling these time periods.

What I really want to know is are they normal? Do other people's systems turn on and off less often than this?

 

[JohnD]

should be less often. if your room stat is controlling it, maybe your hall is very draughty and gets cold very fast, or the stat is to near a window or draughty door.

maybe prop a thermometer by it and see how much the temp varies.

most stats have a fair lag between on and off.

 

[chrishutt]

The boiler in heating mode cycles from off to on in 3.5 mins, so about 5 mins from off to on sounds about right allowing for a lag waiting for return water temperature to drop.

 

[JohnD]

But surely "I have a Danfoss room stat in the hall and this is what is controlling these time periods." means that the hall has come up to temp, and the room stat has stopped calling for heat... but it is calling again after just 5 minutes.

Must be a very small rad to get cold in that time.

 

[Agile]

That sounds about right to me when the outside temperature is about 5°C.

If the outside temperature falls to -1° then the boiler will stay on for longer.

If you want to lengthen the boiler firing time then turn down the boiler stat if its a modulating model.

If not then there is little point in changing any adjustment as its about spot on at the moment IF the boiler fires for all that time.

Tony

 

[chrishutt]

But surely "I have a Danfoss room stat in the hall and this is what is controlling these time periods." means that the hall has come up to temp, and the room stat has stopped calling for heat... but it is calling again after just 5 minutes.

Just because the OP says that doesn't necessarily mean it's true. The OP is keeping his cards very close to his chest. He won't tell us what temp the room stat is set to or what type of boiler he has and what temperature setting he has on that, and watches us floundering around trying to work out what is going on. My guess is that it's the boiler stat that is controlling the cycling hence the fairly regular intervals.

 

[Old_Badger]

Thanks for your ideas so far. I wasn't trying to 'keep my cards close to my chest'!

The room stat is set at 20c. The boiler is a greenstar RI and its temperature is difficult to tell because there are no calibrations. My pipe thermometer says it goes up to about 70c.

It is definitely the room stat that is in control. If I disable the accelerator on it then the cycle increases from 9 minutes to 30 minutes.

The radiator in my hall is too big if anything. This could be the problem. It may be getting my hall up to temperature and turning the boiler off before the radiator gets really hot.

 

[chrishutt]

So is there a problem? If the hall stat is shutting off before the rest of the house has had a chance to get up to temp then you can either turn the hall stat up or restrict the flow through the hall rad so it takes longer to get hot (or both). You can even turn the hall rad off completely if the hall will get enough heat indirectly from adjacent heated rooms.

 

[Agile]

Turn your boiler output temperature down about 5° anticlockwise and then measure the cycle time.

Repeat turning it down until its on for most of the time say 80% to give a little reserve for colder days.

Tony