Pump running but no power to boiler

[Joseph C]

On a breakdown which is stumping me.
The boiler has no power to it even though everything else in the system is working as it should.
The 3 way moves across when it should and kicks in the pump but there is no power on the wire entering the boiler.

 

[John.g]

Is there 230V on the mid position valve orange wire when it moves across and is the boiler a heat only boiler with a external circ pump? With CH only on then there will only be power on the orange wire when the roomstat is closed.

 

[Chuck]

If the boiler has no power to it, i.e. has no mains supply, everything connected to it should be dead as well. If this is not the case, someone has 'stolen' a permanent live, e.g. from a convenient ring main, and injected it into the controls at some point. Systems like this often have a have-a-go amateur doing a DIY repair at some point in their history and have been left in a working but dangerous condition.

Proceed with great caution. Even if the wiring seems dead, something like a thermostat switching on might unexpectedly energise it.

Edit: After a cup of tea, it occurs to me that you may mean that there is no demand signal from the valve back to the boiler, which is a different problem. If so, my warning is irrelevant but I know one guy who had their hand seriously burned by such a system and so I am very alert to the risk.

 

[Deleted member 120897]

As per John, you need to check the outgoing orange voltage, as this should be approx 240vac when calling for hot water, heating or both, then once this is confirmed, you need to check voltage on other wires too.