2 three port valves with boiler running constantly

[mole2006]

Hi Guys,

I've just looked at a heating system which has a few issues like immersion stat faulty.

This is the current set up -
Upstairs has H/W tank (that also feed downstairs) and heating both fed via a 3 port valve to a pump down by the boiler.

Downstairs has heating fed via a 3 port valve but with only heating side wired on the valve back to a second pump by the boiler just for downstairs. The port 'B' on the 3 port valve is plumbed but I have a feeling it doesn't go anywhere but haven't traced it. I've shut off a valve on this leg to see if anything stops working.

The client says rads are heating up with all programmers switched off.

The main issue is the boiler is on permanently and the only way I can see to control the boiler is through a relay.

Is there an 'off the self' relay box to connect both pumps to switch the boiler?

 

[davesparks]

Open the valve you shut ASAP as it is most likely the designed bypass for the system relying on the 3 port valve defaulting to open on the DHW port.

Is this a brand new system which doesn't work? Or is it an existing system which has developed a fault?
If it's a fault on an existing system which has previously worked then you need to find the fault and fix it before worrying about adding relays or whatever to alter the way the system works.

If the boiler is firing constantly then it must be receiving the fire signal constantly, so carry out some tests to see what is giving this constant fire signal. From your description I think you have three possible sources of the fire signal, the 2x valves and the cylinder stat.
Once you have established which of these is responsible then you can move back through the control circuit to establish whether the fault is with that component or further along the circuit.

 

[mole2006]

It's an old system which has been added to. He said it's never worked properly.
There is no switching for the boiler, it's left to turn off when it gets to temp.