Potterton Prima F CH runs for 8 mins bubbles then cuts out

[cannotfixit!]

Hello,
Can anyone help?

We have hot water which is running normally. However, when the CH is switched on it ignites and runs quite normally for around 8 mins or so at first then makes a rather loud bubbling noise sort of bangs and then shuts off tripping the reset switch.

I have bled the system as I thought there was air in the system.

Once you switch the CH back on again it comes on again for a few minutes and then trips again.

Only the rads first off the run are getting 'slightly' warm the others are staying cold because heating is not on long enough to warm them.

Someone suggested the pump, but surely the hot water would not be working if the pump was not working would it?

Any suggestions would be greatly appreciated before I have to call someone out.

Please help quickly kids are moaning about cold!!

Cheers

 

[Gasguru]

Perhaps a blockage in the heating circuit but the pump could be full of debris, the hot water circuit offers less resistance to flow so may still work.

Are you sure it's working OK on hot water...the immersion heater hasn't been switched on by mistake.

 

[jimmis]

probably a blockage?checked the rads have water in them, check that the expansion tank in the loft has water in it, also if it does have water in it, tie the ballcock up so it does not refill straighway pen all the rad valves and lockshields with the system off including the zone control valves if you have any turn them on to manual and then drain down a bit of water from the lowest drain point if the level of the water in the tank in the loft drops as you open the draincock downstairs it eans the cold feed is fine, and you porbaly have a blocakge somewhere, I had to backflush mine with mains pressure to get rid of alot of gunk in the rads , and then refill and then drain and then refill and it came back to life

 

[cannotfixit!]

The hot water is working fine.

I just tried the CH again and this time it only stayed on for 2 1/2 mins before 'bubbling' and then cutting out. It trips the reset button on the boiler.

 

[cannotfixit!]

I have bled all of the rads, they are all ok. Cannot understand it at all. Will try all you suggested. Cheers.

 

[gas4you]

Is this a fully pumped system? I'm not sure about what these boilers could run as.

If it is, check the ch zone valve has not jammed. Have you not got a by- pass valve fitted?

 

[tryitandsee]

Turn off hot water if you can, (turn cylinder stat down, one way of doing that). Someone turn heating on (turn up room stat), another person check to see if pump starts/spinning. If not, I would suspect heating zone valve's micro switch not operating the pump.

 

[bengasman]

gatevalve or similare in dhw circuit? if so, open it 2 turns