Potterton Performa 28 - Differential Valve Problem?

[Mac47]

Hi there,

I have a Potterton Perfoma 28, which is having some 'issues'. I suspect it's something to do with the differential valve, but I thought I'd get some expert advice on here.

When I use the hot water for a long time, when running a bath or having a shower, some of the radiators in the house get hot. Also, the hot water never seems to get that hot.

After doing a little research, it seems to point to the differential valve (I'm assuming that's the same thing as the 'diverter' valve), but would like to get some other opinions in case it's something else.

Also, is this something that I can change myself or will I have to use a Gas Safe person?

 

[petit_pablo]

Differential valve and diverter valve are different parts.

From what you describe, it say the diverter is seized. You don't need to be gas registered to change this water part on your boiler.

 

[Mac47]

Ah, my mistake. What is the difference between the diverter valve and the differential valve? I can only find mention of the differential valve in the Servicing Manual.

 

[Agile]

The diverter valve is primarily the part on the left. It transfers the heated water to the rads or the hot water heat exchanger.

The differential valve is probably referring to the part to the top right of the diverter valve which proves that the pump is working and when its switch is operated allows the ignition sequence to proceed.

But it could also refer to the front section of the diverter valve which is supplied by two small tubes and pushes out the pin at the front to operate the DHW demand switch.

When there is a demand for hot water the front section moves forward and the rear manifold part the moves forward under the pressure of springs inside.

Except that in your case it does not fully move because it is sludged up!

Commercially I always change the manifold section.

Tony

 

[Mac47]

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• Mac47
• 29 Jun 2014
• 1

This is the page in the service Manual with the Differential Valve. Where is the Diverter valve in relation to this? How can I tell if it is working properly?

 

[petit_pablo]

That's a system boiler part that you have posted.
The system variant doesn't have a diverter.

Is your boiler actually a combi or a system boiler? Have a you got a HW tank?

 

[Agile]

Your boiler is apparently a Performa HE !

Is it an "instant" version?

Tony

 

[Mac47]

It says Performa 28 on the front! It was already in the house when we moved in seven years ago.

Hang on...I've just realised whilst I searched for a Performa 28 User Manual & Service Manual online, the link I clicked on led me to the pdf of an HE

Give me a minute.....

Right, I've found a Installation Manual for a Performa 28i. Will that be pretty much the same?

What does 'instant version' mean? It's definitely a combi. No water tank in the house.

I've taken a photo of the insides of the boiler, and have found the right page from the Installation manual (sorry it's on its side!).

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• Mac47
• 29 Jun 2014
• 1

 

[Mac47]

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• Mac47
• 29 Jun 2014
• 1

 

[Mac47]

Hmmm... just had a good look, comparing the page from the manual with what I can see in the boiler and it doesn't look the same. I'll have to do a bit more searching for the right manual.

 

[petit_pablo]

That big brass section is the diverter valve. That will be stuck half in heating position.

You can either service the valve or replace it.

 

[Agile]

Your boiler is the plain Performa and not the HE and not the instant.

My first posting above relates to your boiler!

Tony

 

[Mac47]

Thanks Tony. You're a great help. I've also found the correct Installation Manual now, so that's a bonus!

It says "The diverter valve assembly comprises of a
central heating pressure differential valve and a
domestic hot water pressure differential valve.
These are connected to a manifold which is
joined to the plate heat exchanger"

From what I can work out, the hot water differential valve is the disc shaped one with two skinny copper pipes coming out the top of it, closest to the front of the boiler. And the central heating differential valve has a skinny pipe coming from the back of the boiler and this sits on top of the manifold. Is this right? And which one is knackered?!

 

[Mac47]

Ok, so I've now opened up the boiler and tried to work out what's going on. When I run a hot tap, both pins extend from the differential valves and make their respective microswitches. This happens even when the selector switch on the front of the boiler is set to 'hot water' only. The radiators also get hot.

When I turn the selector switch to 'hot water & central heating' and then turn on the central heating via the wall thermostat, only the differentail valve that sits on top of the manifold operates.

I'm guessing the central heating differential valve is knackered and needs servicing/repair/replacing. Am I barking up the right tree?

Also, what would cause the central heating differential to operate when only the hot water is required (just curious!)? Not sure if it's relevant, but I live in an area with very hard water.

 

[petit_pablo]

It's not either of the differential valves it's the main body of the diverter that's the problem. I've said it enough times.

The front diff valve is for HW. The one ontop, with the small pipe is the pump differential, not a heating one.