Potterton netaheat type boiler, banging from pipework after running for a few minutes.

[hazeman]

I have a SIME SUPERIOR 80 boiler (a variation of potterton netaheat). This is mounted in an outhouse. This is a conventional system with a hot water tank. Its been there for 20 years and apart from the odd fan has been fine.
Last night the frost guard thermostat kicked in: Once at 3AM when it switched off and then at 6AM. It woke us up because there was a lot of banging and gurgling from the around the HW tank where the pump is. I switched the system off at this point. The HW tank temperature was boiling hot. Obviously the system had ran really hot without the rads in the circuit (there is no pipe stat outside to limit it).
I've disconnected the frost stat and let it cool a bit. I had to reset the boiler also.

Now when I run it, it runs for a few minutes (the boiler fires up and is heating water) but then the banging from the pipes starts again. I turn it off at this point. The reset on the boiler has also tripped.
I've tried this about 5 times with just HW and also with CH.

At the moment its been cooling all day. There is water in the header tank.

Does anyone have any advice please?

regards
Liam

 

[cross thread]

Pump running ?

 

[ianmcd]

As above sounds like the pump has jammed

 

[gas112]

Yep pump has had it
Check header tank in loft has got water in it and ball valve has not stuck