Hopefully an easy boiler question...

Hey guys,

So I’ve had a suspected problem with one of my motorised valves not opening and thus not allowing heat flow through the downstairs loop.

I think I know how to fix it (replace head on valve) but when thinking about the wiring etc it got me wondering a few things:

1) What does my thermostat physically activate? I’m positive it doesn't trigger the boiler directly.
2) If the “request for heat” signal to the boiler isn’t triggered by the thermostat, where does the signal come from?
3) The pump seems to start when any of the thermostats request heat, is this simply triggered by a branched signal wire from the thermostats?

My setup:
Ideal Logic H15 Boiler
Hot Water Cylinder (1 coil)
2x Siemens Battery Powered Thermostats (RDE100.1)
3x motorised valves
1 Grundfos pump

I studied the pipes in my airing cupboard and put together a diagram which I *think* is how my heating system works but I'm not sure. Anyway here it is:



If anyone can help me get my head around signalling / what triggers the boiler / pump / valves / etc that would be great!

C

Here is the wiring diagram for a S Plan plus system (two heating zones, plus hot water). As you can see the thermostats operate the MVs, which have internal microswitches to control the boiler/pump.

When the thermostat demands heat the MV opens and it’s switch turns on, connecting boiler and pump so yes it does activate them.

Nice one thanks guys Sorry for not replying.

So then if I understand right, that the microswitch in the valves are simply activated by the current that the motorised heads receive, and this in turn activates the circuits for the pump and boiler simultaneously

Yes but Is this leading to somewhere?

Basically was trying to ascertain where precisely the failure occurred but through trying to understand how exactly it all works.

E.g. So theres no direct wire from the thermostat to the boiler to send a heat demand signal.

Also if the valve motorised head is broken, I’d have thought the chances of the microswitch also being broken is pretty slim, but seeing as the boiler isn’t receiving a heat demand signal, the microswitch wire must be in series with the head.

Ultimately I don’t want to buy a new head only to find it was just the microswitch, or vice versa if you get my drift. But also I didn’t want to be messing with the wires in the valve without knowing what the grey and orange wires were for

Understood but you’ll still need a new head for a microswitch. If you’re competent you can just make the micro switch and see if it sends a signal

Charlie D said:

Nice one thanks guys Sorry for not replying.

So then if I understand right, that the microswitch in the valves are simply activated by the current that the motorised heads receive, and this in turn activates the circuits for the pump and boiler simultaneously

Click to expand...

The microswitch in the valve should have a separate live feed, (as on the wiring diagram above), not the live that comes from the thermostat.

Normally the thermostat operates the valve. Microswitch on the valve is electrically separate and takes the control loop from the boiler. Usual method is to wire all microswitches in parallel so whichever valve opens will bring on the boiler.