Boiler banging and pressure fluctuation

nickem

I have a Potterton Promax combi HE Plus, which is about Three years old.

The central heating appears to be fine, however when I run the hot water I get a a horrible knocking/banging sound from inside the boiler and the pressure fluctuates between 1 and 1.5 bar, the noise stops as soon as the hot water tap/shower is turned off and the pressure immediately stabilises. This does not happen all the time I would say about 1/3.

My questions:
Is this likely to be an air lock, if so how can I remove it from the system?
Could my pump be at fault, should I call an engineer?

Please see clip below showing issue:

http://www.youtube.com/watch?v=tyPWUU2DVdk

gas4you

The boiler is overheating due to lack of flow for some reason or another.

First thought would be the pump, but you say the heating is working?

I can think the other possibility would be the plate HE blocked if the rads are actually working properly

nickem

Thanks for the quick reply - Is this dangerous?

If it is the plate can this be cleaned or does it have to be replaced?

Also is this something that has to be done by a heating engineer, any idea on the expected cost of part and replacement?

Kind Regards,

gas4you

Depending on the problem, the plate could be chemically cleaned, but as Potterton parts are some of the most reasonably priced around, it could be better to replace, but you would need someone in front of the boiler to confirm the fault before spending any sum of money.

Are you 100% certain the pump is working properly?

nickem

I appreciate your comments on this matter, you have been a great help. Is there a surefire way of knowing if the pump is working correctly, It would be nice to eliminate it?

Kind Regards

garethgas

Proving the pump is ok isn't as straightforward as it might seem. There are lots of other noises going on so it can be tricky unless you can remove the centre screw and see the shaft spinning.
Also, it might be intermittent so although you check and confirm its working, it might still be the cause.
I'm suprised though that your not getting any error codes showing up.