Potterton Puma 80 combi pilot out after about 1 minute

[Tony59]

I have a Potterton Puma 80 combi boiler about 4 years old. If I light the pilot, then run the hot water, it fires up. But the flow rate stays low. Then after about a minute the pilot goes out. After that if I run hot water, it is still low flow rate but very hot. Similarly, if I light the pilot again, then I run central heating, the boiler fires up but the flow and returns stay cold. Then after a minute the pilot light goes out. The low pressure light never comes on and I think that the pressure level is adequate. The fan works and the steam release valve (on top of boiler) is loose. I think that the boiler overheats and pilot cuts out because it is not allowing any water to flow whether CH or HW. But I don't know how to isolate the fault. Any advice would be appreciated, thanks.

 

[ChrisR]

If it fires up the heat is going to the CH. Run HW and feel the fat pipes and first rad.
That's what happens if the Domestic Hot Water Flow Switch sticks on. Has been described many times - do a search here, check for the red light on the pcb.

 

[Tony59]

Thanks for the reply. I did not find another reported case the same as mine, as the ones I read reported that either HW worked or CH worked.
The CH pipes (and radiators) were cold.
In my case neither worked and the pilot light went out after the boiler firing up for about a minute. I got the diverter value changed, descaled the heat exchanger and other internal water pipes and the boiler now runs as desired. We also had to replace some O-rings and seat the heat exchanger properly, as it was previously leaking water, perhaps for sometime as there were corision marks where the leak was coming from. Looking at the old diverter valve, it appears to be stuck in a position where neither HW nor CH can flow. It seems to be sludged up. Better clean the CH system to prevent anything else sludging up.