Ravenheat LS80T knocking noise then shutoff

[zappa69]

Any advice gratefully recieved:

Whenever I either turn on the DHW tap or CH the boiler will fire up and the fan will start but after around 5-10 secs the boiler will make an dreadfull clunking noise and will stop the ignition/flame

There does appear to be a small amount of water discharged from the outside valve.

If I turn the thermostat right down on the CH it will fire and stay fired until it reaches the requested temp - However if I keep turing the thermostat up it will cause the clunking noise and the boiler will cut out.

I have looked at the plate heat exchanger and DV and they both appear to fine (water flows nicely through exchanger) free movement in DV - no really sure how else to check DV ??

Can anyone suggest what else to check ??
Is there a way I can check the pump functionality ?

Thanks

 

[Agile]

Look at the FAQ on this site for the finger test for the pump.

Thats involves exposing the impeller so any dirt on it will be seen.

It might be sludge or lime scaling.

Tony

 

[zappa69]

Many thanks Tony

The test indicates that the pump is not functioning. It is not spinning up at all. If I were to take the pump of to have a look at it's internals can I take it off without draning the boiler ??

 

[ServiceNumpty]

No it will need draining down.

 

[zappa69]

I have taken the pump off and had a look and it moves freely and power is definitely going to pump. Am I correct that if the pump has power then it should be running, there isn't anything on the pcb which sends a signal to the pump that starts it?? Can anyone think of anything else, to me it looks as though the pump is the culprit.