Hot water comes on, but not the heating; thermostat fine…?

[edstevens]

Hello all,

I could use some help here. My central heating doesn't come on when its meant to.

The thermostat appears to be fine. Using a multimeter I get 240 V across the live and neutral; 240 V across switched live and neutral when thermostat is on and the neon light glows; and 0 V across the switched live and neutral when thermostat is off and the neon light doesn't glow.

The hot water is working more or less normally. Boiler and pump turn on when the timer tells them to. Boiler switches off when it is supposed to, but the odd thing is that the pump switches off at the same time as well, rather than "overruning" for a while afterwards.

There is a link inside the Honeywell Wiring Centre that the instructions say needs to be cut when an overrun is used. I did so, and nothing worked at all. So I've tied those wires back together, and the heating at least is operating normally, except for the lack of overrun.

Two background factors. One of the two microswitches inside the three-way port is faultly. Although annoying and needing to be replaced soon, I can't see why this would effect whether or not the central heating comes on at all. The second factor is that I have replaced the wiring centre and the hot water pump, and it's not beyond the realms of possibility I've not rewired things properly.

Any ideas of particular wiring problems that would cause this particular set of symptoms?

Cheers, Ed Stevens

Hardware: Baxi Solo PFl 30; RS Thermostat; Honeywell Sundial Plan Wiring Centre; RWB9 Timer

 

[kevplumb]

is the pump wired from the boiler

 

[TicklyT]

..... One of the two microswitches inside the three-way port is faultly.....

Would that be a microswitch that shifts the control of the system from the hot water cylinder stat to the heating room stat when the HW stat is satisfied by any chance?

 

[Agile]

I dont think they put microswitches inside the three port valves just for fun!

 

[MANDATE]

Both micro switches affect the CH.
Valve cannot move beyond mid position without power from the grey wire which would be prevented if switch No 1 has faulty contacts.
Even if switch No 1 is ok and valve can move fully to CH position, power out of valve through orange wire would prevent the boiler from lighting if the micro switch No 2 has faulty contacts.