Combi boiler overheat or overrun problem

hockey2019

You are correct pump does work fine - checked it at it starts ok - checking the diverter that moves up and down when switching between heating and water - could it be a flow switch ? 

Albermarle

@FreeBear
@ThisIsWeird

Can you help the OP ?

FreeBear

Albermarle said:

@FreeBear
@ThisIsWeird

Can you help the OP ?

To remove the cover on a WB Greenstar requires breaking the seal around the casing. That requires a Gas Safe engineer as the average home owner will not have the tools & equipment to check that there are no leaks once the cover is reinstated.

A few boilers, you can gain access to some of the workings without disturbing the seals and it is possible to undertake certain repairs. But unless you have knowledge of what can be done safely without falling foul of the regulations, I would still recommend calling in a Gas Safe engineer.

Make a mistake with any gas appliance, and it could result in a big bang leading to destruction of property or even death.

ThisIsWeird

hockey2019 said:

Thanks will try that - should the pump start straight away when heating is called for - as it seems that the boiler fires up but - water probably not being circulated so heats up and boiler stops heating as it reaches temp then stays at that temp for a while only slowly dropping 

Pretty sure, 'yes'.

If you stand near the boiler when the 'stat calls for CH, there should be a very short (a second?) zzzzp as the diverter motor moves the diverter valve to CH position, followed immediately by a 'click' and the pump and boiler firing up, the pump being indicated by the sound of slooshing water.

Some or all of these might not be very noticeable depending on the boiler, and the very first 'zzzzp' of the diverter valve might not occur at all if the valve was already in the CH position - so you can try first running a hot tap for a second to move it to DHW position, turning the tap off, waiting until the boiler shuts off, and then operating the room stat.

As FreeBear suggested earlier on - or was it NFLO? - this could be a sticking diverter valve, or a failing pump. Or other stuff.

Beyond the investigation of a layperson, I'd suggest - it's delving into the innards.

Albermarle

FreeBear said:

Albermarle said:

@FreeBear
@ThisIsWeird

Can you help the OP ?

To remove the cover on a WB Greenstar requires breaking the seal around the casing. That requires a Gas Safe engineer as the average home owner will not have the tools & equipment to check that there are no leaks once the cover is reinstated.

A few boilers, you can gain access to some of the workings without disturbing the seals and it is possible to undertake certain repairs. But unless you have knowledge of what can be done safely without falling foul of the regulations, I would still recommend calling in a Gas Safe engineer.

Make a mistake with any gas appliance, and it could result in a big bang leading to destruction of property or even death.

Although some ( all?) Greenstar models have casings with holes in them, so are not actually airtight at all.

Technical Bulletin 151 - Registered Gas Engineer