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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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Rick, I have a Potterton Suprima 50. I have just replaced

Customer Question

Hi Rick, I have a Potterton Suprima 50. I have just replaced the PCB and it has been running fine for a couple of weeks on Hot Water mode. I think, if I remember rightly, that I tried it on Central Heating mode after replacing the PCB, but I can't remember whether I ran CH and HW together or whether I ran CH on its own. At that point the rads got hot and I switched it off.
Tonight we actually needed to put the central heating on, and it doesn't work. The boiler won't fire. It still fires absolutely fine for HW, but when CH is on, on its own, the boiler is off and the rads are cold.
I have what has been explained to me as an 'inverted' tank, which has its heat exchanger the other way round from what is conventional, though this name has been disputed by another plumber! Anyway, the tank has two blue British Gas motors (located in two pipes coming out of the tank). When switching on the HW one of these motors makes a noise (and then the boiler fires up). When switching on the CH, the
Submitted: 1 year ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 1 year ago.

It sounds like the central heating 2 port valve has failed. Can you put the central heating only on and tell me if the lever on the side is slack or tight?

Customer: replied 1 year ago.
Hi there, please be a little clearer. Which lever, on the side of what?
I do not appear to have a two port valve. I have read a lot about this component but I cannot find it anywhere. I have looked high and low in the airing cupboard and inside the boiler casing.
My system has two pumps (British Gas Multihead G). One pumps the hot water and the other pumps the CH water. Both work when they are supposed to. If the water in the tank is already hot (which it will be after the HW has been on for a while) the CH pump pumps the CH water round the radiators which get warm. However, the boiler doesn't fire at any point and the radiators will cool down again as the heat is lost from them.
Do you think it's possible that I don't have a 2 port valve because I have two pumps? If this is impossible, please could you give me some idea of where this valve is located?
Customer: replied 1 year ago.
I have also tested the room thermostat with a multimeter. I'm getting a voltage when it's turned up high, and not when it's turned down low. I can also hear the pump start up when I rotate it from low to high temp, and off again when I rotate it back down.
The two pumps seem to be working. I have tested with a multimeter and there is voltage at the terminals when there is supposed to be. Both pumps make a noise (quite, but audible up close) and it is possible to feel the pipes vibrating when the pumps are running. Furthermore, the CH pump is definitely pumping water through the radiators and the HW pump is definitely getting the hot water to the taps.
Customer: replied 1 year ago.
Do you think this could be caused by a PCB issue? This was replaced two weeks ago.
Expert:  Andrew Smith replied 1 year ago.

Let's take a step back.

The Potterton Suprima is a heat only boiler, are you referring to something else in the airing cupboard - do you have a heat store and if so is there any name on it?

Customer: replied 1 year ago.
There is an insulated tank in the airing cupboard. Presumably that is a heat store? It doesn't have a make written on it.
If you like I could send some photos?
Customer: replied 1 year ago.
When I asked the question, I clicked the box saying I wanted an answer 'right now'. This implies that I wanted an answer within minutes of asking the question. This was last night! Could you tell me why there are literally hours between our replies?
So far we have got nowhere with this. Your help would be appreciated.
Expert:  Andrew Smith replied 1 year ago.

it takes time for the email to reach me and i respond

Can you upload a photo?

Customer: replied 1 year ago.
Hi Andrew,
Here are some photos. The tank is pretty tall (about 1.5m) and so I've taken a couple of photos of the bottom and a couple of the top. I've tried to get all the pipes/wires/pumps into the photos plus the timer controller. In the loft there is another tank of some sort, though I'm not able to get in there to have a proper look.
Customer: replied 1 year ago.

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