Central heating/Pump/boiler problem

[paulride]

Is the circulating pump for the hot water as well as the central heating?

I have just changed my programmer from a danfoss to a sunvic and at the moment I can only get the boiler to come on when I hit the hot water button on the programmer.

The sunvic is meant to be able to fit straight on the old danfoss backplate so that no moving of the wires is needed.

The other thing is that I changed the pump because I noticed it wasn't working after the boiler kept shutting down after about 3 or 4 minutes.

Now I have changed the pump and when I flick on the central heating on the programmer the boiler dosent fire up. It will only fire up for the hot water and then only for a few minutes.
So the boiler is still shutting down prematurely

 

[D_Hailsham]

Is the circulating pump for the hot water as well as the central heating?

Do you have any motorized valves after the pump?

You could have one, as on the left, or two, as on the right.

If so, the pump is for the hw and the CH.

I have just changed my programmer from a danfoss to a sunvic and at the moment I can only get the boiler to come on when I hit the hot water button on the programmer.

The sunvic is meant to be able to fit straight on the old danfoss backplate so that no moving of the wires is needed.

Some programmers have a switch or similar on the back which says "pumped" and "gravity". If your pump is in the circuit to the HW cylinder you need the switch on "pumped" but, if not, it needs to be on "gravity".