Potterton 24 Differential pressure valve replacement, how?

1 Nov 2009
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United Kingdom
I have recently had a leaking Differential pressure valve on my Potterton Performer 24 boiler. I've replaced the whole valve and everything was great , no leaks, DHW working fine, until I tried the CH. Now the CH fires up and runs for a minute before cutting out. There is hot water leaving the boiler but it's not reaching the radiators.

My question is, what did I miss ? Does the pushrod that passes through the front and rear of the valve need to be lined up with something in the diverter manifold ??

Thanks in advance.
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Its not clear to me exactly what you have done.

If you only changed the flattish front part the the rear manifold part may be jammed in the DHW position.

Or you left a CH valve underneath closed.

Or the CH return filter is clogged.
Just to clarify, I replaced the DHW Pressure Differential valve (part no 248063) that is held to front of the manifold with two grub screws. I turned off the mains water inlet, emptied the hot water circuit, unsrewed the two sensing pipes and then replaced. I then turned the mains water back on let water into the boiler and then opened the hot tap. All the valves to and from the boiler are open again. Everything is working fine on the DHW side.

When I switch on the CH the Central heating pressure differential valve operates the switch and CH heating kicks in as usual. The CH "flow" pipe leaving the boiler gets hot but then after about a minute the boiler turns off.

Could it be a coincindental pump failure? The pump is spinning but how do I know it is moving enough water through the system ??

It must be something really simple as 90% of my boiler is working OK, just the central heating flow isn't good.

I'm stuck and would be really really apprecitive of any fault finding tips or advice

Thanks very much for reading this.

P.S there's a least a drink in it for anyone who can give me the correct info to fix this !!!
Shut the gas off and run the hot tap. Feel the plate heat exchanger at the rear of the boiler. When it's cold shut off the tap. You may have to reset the boiler several times to keep the pump running.

Now turn the gas on and run the heating. Feel the plate...it may get a little warm on the left but if it's cooking hot the rear section of the diverter is sticking.

Otherwise could be the return filter is clogged as Tony said earlier.

Got TRV's on the system? Pins often stick down after the summer.
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I'm with Agile, sounds like a circulation problem, pump must be ok or you wouldn't get hot water, recheck the heating iso valves and the strainer in the return, could be a fault on the main part of the diverter valve ;)
doubt if pump failure. Pri flow switch operating to fire blr in both modes.
Diverter valve spindle shouldn't be trappped in dhw as i think it is pushed into CH by pin of Press diff ass' and is allowed to travel forward when PDA moves when tap opened.
Are all your rad valves open- both sides? Obvious I know, but worth the question
Check your return filter as suggested above
Without electrocuting yourself, have a feel to see if the water if the bypass is getting red hot. (runs behind the plate heat ex between the diverter valve assembly and the hydraulic inlet ass'- behind pump.)
Thanks everyone for taking time out to give advice, much appreciated.

rojaca - your theory about the spindle sounds most likely. Does anyone out there know for sure if the two pins, one on differential and one on diverter valve, are supposed to align and therefore move together?

When I put the pressure differential back on I didn't do this as it was not mentioned anywhere in the instructions. I'm thinking that was my mistake and now the pins are missing each other leaving the valve in DHW mode? I'm going to take it off again and refit paying attention to pins.

Also if this is this case how are you supposed to line up two pins (2mm diameter) inside a metal casing where you can't see them?

Thanks again and I'll let you know how I get on. Will confirm who gets the drink !! :)

Just for the record since the last time I wrote I checked the pump and its spinning ok. Also I double checked all valves at the boiler are open and went round all the TRV's to check none are stuck.
You will be wasting your time!

It seems some of my posts are invisible.

I wonder how I can solve that problem.

Perhaps its because you got mixed up back in 2005 when they said everything had to be condensing.
And you miss heard and thought they said condescending :rolleyes:
If press diff is in housing, then pins will be lined up. Was only a thought for discussion as to how the spindle acts upon the various components within the valve.
Yes rojaca, the pressure diff is in a housing. This housing (part no 248063) was the part I detached from the rest of the change over valve. Presumably when the two are assembled in the factory to create one large unit then everything is lined up perfectly.

I apprecite you setting it up for discussion, that's exactly what I need.
What I mean is the pins WILL be aligned if you've got the front press diff (248061) assembly screwed back into position on the front diverter valve (248062).
If you do the check as outlined by Gasguru regarding the plate htex and quickly check the bypass pipe to see if either of these is getting hot then you can be fairly sure its your diverter valve. If not, as has been said before, you're looking at a circulation issue.
BTW when you changed the Press diff ass' did you just knock off the cold in. If you closed the two outer heating isloation valves, check that the plastic heads haven't turned but left the actual isolation valves turned off
Cheers everyone, first pint to you rojaca. I took the two grub screws out and readjusted the fitting of the differential valve. I didn't have it pushed tight up against the changeover valve, my mistake!

I've refitted it tight up and now the CH fires up properly and runs for a little while.

However, only the upstairs radiators are working, the two downstairs are stone cold.

I'm going to review all the posts and follow your various tips (yes , even yours Agile!) and fault finding advice. Will do that this weekend, at least We've got 70% heating back, god it's been cold, you don't realise how good CH is until it's off !!!

Anyhow cheers again everyone and I'll let you know how i get on.

In the meantime keep the ideas coming !!!

Probably just air , turn off upstairs rads to force heat down stairs

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