Boiler constantly cycling

14 Jan 2012
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United Kingdom

I believe there is something wrong with the way my boiler is operating and wondered if you guys had any ideas?

I have an open vent system with a Worcester Bosch 19/24cbi boiler.
The problem is that although the boiler ignites fine and seemingly runs ok, after an initial period of about 20 - 30 mins of central heating or heating the hot water, the boiler then begins to cycle. it will then only run for a couple of minutes at a time, the burner then extinguishes despite the stat still calling for heat. You can hear the fan in the boiler run on. Immediately after the fan in the boiler stops, the boiler goes through its cycle of running for 2 minutes or so again.

Also, although it is quite a big hot water cylinder the water which is timed for an hour in the morning, it seems to take the full hour to reach the temp (60c), normally having also gone through this cycling process for 40 mins or so. At the same time the hot water is being heated, I can hear the movement of water in the central heating system by the radiators, is this normal? The diverter valve indicates hot water only and the radiators never get hot during this time.

Any thoughts or ideas much appreciated!

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Hi Dan,
The boiler stat on the front is set in the 3 o'clock position. There are no numbers on it just a gradual increasing scale and it is set to the round dot. The scale finishes in the 5 o'clock position. It just seems strange to me than it cycles on and off so frequently, in seems very ineffectual and not good for energy efficiency?
Thats what happens when a boiler is oversized for the load !

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Is there a solution?
Can I just turn the boiler stat down or turn on all radiators / increase pump speed? Could a gas engineer regulate the gas pressure to aid this?
Thanks and regards,
Yopu are confusing hot water heating and central heating in your questions.

Its difficult to give you a defiunitive answer unless you can measure the actual flow temperature from your boiler.

To do that you would need a contact thermometer!

Hi Tony,
Thanks for the reply. Sorry for getting the systems confused. I was just trying to give all the info I had and to show that the boiler was cycling a lot on both central heating and when heating the hot water.
I guess I'll have to try to get hold of a contact thermometer then.

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