Boiler Cycling On and Off

[hontoir]

Hello everyone,

Unfortunately this is my first post, and I have a lot to learn..

Hopefully someone can point me in the right direction, I have a general interest in all things engineering, however, will happily accept when enough is enough and call in the experts.

So, I have:

Boiler - Halstead Wickes 102 Combi (currently set half way between Min and Max on CH and HW)
Thermostat - Honeywell CM901 (set to 17 degrees) (room temp currently 13 degrees)
Rads - 9x (all fitted with lock shield valves)

With the above setup the desired room temperature is not being achieved (according to the thermostat anyway) and the boiler is cycling on and off.. All radiators appear to be reasonably warm.

The cycling involves a short pre-purge then firing.. Then once the firing finishes it switches to a post-purge.. As soon as the boiler completely shuts down it restarts within a second.

There are no issues with the HW, the boiler will stay on for the duration of a long shower!

Thanks in advance for any pointers


EDIT
When the system does eventually get up to temperature (takes about 24 hours) the boiler still seems to cycle even though the Thermostat is then reading the same / sometimes higher than the setpoint.

 

[SimonG]

Get a gas safe engineer to have a look. No advice given regard gas appliances on the open forum.

 

[hontoir]

Thanks Simon, so you think it is an issue with the boiler itself rather than a central heating system problem, or an issue with the thermostat?

 

[Dotty]

It's an internal problem. As said, you need a gas man.