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Discuss No hot water and heating comes on! Changed 3 port valve. in the Central Heating Forum area at PlumbersForums.net

I wonder if anyone could help.

Problem: We have no hot water and the heating comes on when we switch the hot water on from the boiler programmer to heat the hot water up.

Our boiler is a Potterton Suprima or (Supr1ma).

What we’ve done so far: My neighbour switched the three port valve so we could have hot water heated up from the immersion tank instead of the boiler .

My brother changed the 3 port valve to the same ‘Center’ 3 port valve.(we had water coming out of the over flow tank in the loft, I think it was the radiator tank,-we think it is a faulty over flow ball valve). We tried another 3 port valve incase the new one was faulty but Changing the 3 port valve - Didn’t work.

My brother changed the boiler programmer (Potterton EP2002 to an Ep2) because the old one had a broken leaver and thought it might be a signal problem. - Didn’t work.

Someone said it could be a wiring problem.

We do have a problem with our shower. We have the shower plug switch constantly off and only switch it on when we want to use it because the shower will sometimes randomly come on and to stop it we have to switch the plug on and off to reset the shower. The shower is a Aqualisa Quartz. Could this cause a wiring problem?

Last year we had the fan replaced in the boiler as it stopped working which caused the hot water from heating up and the heating to come on.

Does anyone have a idea as to what the problem could be?
We only moved into this house 2 years ago.

thanks in advance for helping.


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I'll give you 10/10 for honesty

What made you think that you could make these changes and it would work?

The wiring centre doesn't appear to have enough cables coming from it either

And as for the Aqualisa - unless you've been fiddling with this wiring that should continue to work as before.


A relatively easy fix for someone with experience. I appreciate you and your friends have tried to fix it but some of what you've said above doesn't even make sense.
I suggest you find an engineer to give it a look over, you never know, it could just be as simple as the three port mounted the wrong way round.
Our neighbour has exactly the same setup and had the same problem and he changed the 3 port valve and when we googled; heating comes on when we turn on hot water, all answers pointed to faulty 3 way valve. When my brother changed the 3 way valve it seemed faulty as there was no resistance in the switch.
The 3 way valve is fitted with B to cylinder and A to heating.
As soon as we switch programmer to hot water all 3 pipes connected to the 3 way valve heat up.
In hindsight it probably would have been cheaper to get a pro. Should we cut our losses?
Did the previous setup work at some point?
Yes it was working fine previously, Just all of a sudden the heating started to come on when we switched the hot water on to heat up.
I've had a issue with the aqualisa where the internal valve seize and the unit would either not stop water running or it would come on randomly.

While you could google around and find posts on how to dismantle and put grease on the valves, taking the internals apart can cause future leaks in the unit. I think a replacement is around £200+ if you fit it yourself.

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