Potterton Suprima 80 Airlock

[Marty1966]

Hi, Hoping I can get some help here. Drained down the system today by closing the valve on the F&E Tank outlet to plumb in some new rads.
When finished I opened the valve again but upon starting the boiler up and calling for HW on the primary circuit there became an increasingly violent banging/knocking from the boiler followed by a dry fan sound... at which point I switched HW demand off.
Ive tried this again later and although it took longer to get to the knocking it continued ... Now the boiler wont fire for the HW at all.
(The CH circuit works fine after bleeding the rads)
My question, though I understand from a previous question, there is an air pressure release valve but I suspect this isnt working? Am I correct in my assumption that the problem is an air lock and if so what is the process to bleed this ?
Many thanks

 

[terryplumb]

Look for air bleed valves on the pipework to coil in hot water cylinder.
Check pump for air as well.

 

[Marty1966]

Thanks Terry, Ive been bleeding the bleed point on the coil circuit but its absolute minimal air purging. How/where on the pump do I check for air - is there likely to be a bleed point?
Incidentally above the pump in the pipework theres a wheeled valve that seems to ultimately like the flow and return loop - what exactly is this in a vented system ?
I

 

[terryplumb]

It's a by pass , don't touch it !!
Not sure on bleeding that pump in particular ,but have a look at the back ( may need a mirror) for a silver disc with a slot ,in the centre of the housing.
Is your central heating working ,100% ? If it is the pump will not need bleeding .

 

[Marty1966]

ok - just as well as that red valve would only be reachable with someone with the arms of Mr Tickle! I can feel a slot on the top side of the pump so Ill try to get a pic and confirm with you if that looks like a bleed point

 

[Marty1966]

Sorry, Yes the central heating is working ... now! It starting heating then went into a standby mode so just left it and then heard gurgling from the living room radiator so I went around bleeding the radiators again and it began working again as normal

 

[terryplumb]

As said ,if heatings ok ,pumps ok !! To be honest it all looks so cramped in there ,I doubt you could even bleed the pump !!

 

[Marty1966]

Why would the pump not bang and thump on the when the heating is on ? They are two different circuits but how does the primary circuit carry the airlock when the heating circuit doesnt ?

 

[terryplumb]

You only have one pump ,it either pumps around rads ,or hot water cylinder or possibly both. You said it's the boiler that's making the banging/ thumping not the pump ? If there is air in the system its likely in the hot water circuit ,as the rads are all ok.

 

[Marty1966]

Got a pic of the pump with the slot as you mentioned. Good to know it exists.
So it's therefore the HW circuit thats the issue. If that bleed point on the flow/return (coil) circuit isn't expelling any air worth talking about would it therefore suggest theres possibly insufficient water in that actual primary pipework?

 

[terryplumb]

That is indeed where you bleed the pump ,and you only unscrew it a little ,till water comes out .
Can you show pics of cylinder / coil air bleed ? And when you bleed from it ,let it run water out for a good while.

 

[Marty1966]

I'll get a couple of pics now and Maybe you would suggest changing it for a more usable air bleed

 

[Marty1966]

I opened it just now and no air just spewing steaming hot water

 

[terryplumb]

I am not at all sure that the pipe is connected to the coil. The fitting is a compression stop end ,not an air bleed valve .
Is your programmer currently set to call for domestic hot water ?

 

[terryplumb]

On the pipe marked flow ( on insulation) high up there appears to be a 15mm pipe branched from it ,where does it go, what's on the end of it ?