Gas Boiler constantly going on and off

Folks,

Can someone please help me out here. I've a Ferolli gas boiler and a 2 zone heating system in a detahced two storey. Once the heating has been running for a while the boiler turns itself off and less than a minute later back on again then after another minute it goes off again and so on until the timer shuts the thing down.

Any ideas? I've had the engineer out a few times and the plumber but no joy yet. The house is only a few months old and I'm still dealing through the builder so everything is slowed down and I'm suffering from chinese whipsers I think.

Any input appreciated,

Noob.

Check to see if it is a pressurised system, it may be hovering around the set point, check to see if it is at about 1bar.
There are a lot of other things it could be though.

Make sure there's water in it!!!!
Check the water tank in the attic.
Also check that the pump is working...

My gas boiler works the same but are you sure that it's not just the gas shutting down when the heating has reached the correct temperature, going back on within a matter of mins is due to temperature having dropped which sets the burner back working. Don't know where your boiler is but mine in built in behind the fire in the sitting room (we have no chimney just an outlet), it's very noisy and quiet annoying when your trying to watch tv or talk and this boiler starts clicking on and off and it's def. more noticable during the colder months.

Also could be the room thermostat. Either the boiler thermostat or the room thermostat.
One way of checking is to turn 1 way up and see if the boiler works okay.
If it does then the one turned up may be causing the problems as the other thermostat will have been working properly and controlling the temperature.

Obviously ensure that there is water in the system and if it´s a sealed system air in the pressure vessel . Many gas boilers have integral air vessels which are a little small and some installers can't resist letting some air out to see if there´s any in there. Doesnt take much to deflate it. And some boiler engineers don´t even carry a simple pump to pressurise it.

The differential between the on/off on the boiler stat may be minimal
but you really need competent plumber to see it Preferably a member of the Institute of plumbing. plumbersdiary.com may be of some help to you.

Thanks for all the replies. Very informative. The bouncing only seems to occur whent he system has heated up. Its a sealed system and has water in it and the pressure is about 1.3 bar when running. The rads etc. heat fine it just the constant on and off cycle with 1 min that's the issue.

Is it a big deal to set the on/off differential? I'd have thought the boiler should stay off for 5 or ten minutes once heated up. Thermos. were checked by pumber and electrician and are working apparently.

I'll keep folks posted.

Regards,

N.

Update Re: Gas Boiler constantly going on and off

Folks,

Have done some more testing (after getting a 400 yoyo gas bill for Oct/Nov).

With thermo. off d/s and on max (~30) upstairs the boiler comes on and heats up then after 45 mins or so it starts into its on/off bouncing routine. it continues to do this until it is either switched off manually or, if on timer, the timer cuases it to switch off. At this point it stays off.

It appears to be incapable of staying off when under thermo. control. Bouncing takes longer to start when boiler thermo. and zone thermos are maxed.

Does this info. make it easier for anyone else to diagnose? I'm waiting since yesterday for a response from the builder and from the calor rep.

Many thanks,

N.