Potterton Suprima 50 knocking on shutdown

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I have recently had to drain down my hot cylinder & feed/expansion tanks for minor maintenance prior to the impending replacement of the hot cylinder.

My Potterton Suprima 50 has started knocking & visibly expanding/contracting on SHUTDOWN. The primary pump is wired to the HW valve & does not overrun.

HW & CH seem to be working fine.

Any advice?

 

[AlanE]

Could be boiler not dissipating excess heat at end of demand.

My Suprima manual says and to quote 'Pump MUST [their capitals] be wired back to the boiler'.

I would suggest doing this to start with.

Alan

 

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Thanks.

I had recently done this but as it seemed to make no difference to overrun I returned to the plumbers original wiring setup.

I now suspect the reason it didn't overrun is because it didn't have to! A few days ago I turned up the boiler stat...

I am about to install a new hot cylinder & the manufacturers recommend running the boiler on max. Does this seem right?

 

[AlanE]

'I had recently done this but as it seemed to make no difference to overrun I returned to the plumbers original wiring setup. '

In all probability if the boiler was wired up with the pump supplied from the wiring centre the boiler only has a live supply when there is a demand for heat from it.

The Suprima needs TWO live supplies. One permanant which supplies power to pump on over run and a switched live that is live when heat is demanded.

Without the permanant live the pump overrun will not work it will still switch off at the same time as the boiler.

What you original problem described is a boiler that is unable to get rid of the accumulated heat at the end of its burn cycle. The exact purpose of pump over-run which Potterton say should be connected.

Alan

 

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Thanks.

Potterton have also urged me to rewire & this was done today.

 

[ChrisR]

I shoul jolly well think so. Is the boiler still "visibly expanding/contracting " ?

 

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All is well. Thanks again.

I'm glad this was sorted as next week I fit an Albion Superduty CF45, which I'm told works best with the boiler set to max.