No DHW demand signal

[OptimisticDIYer]

Hello and thanks for any help.

I have a Navien system boiler configured as S Plan.

Everything has been working fine for 2 years until the other day when the boiler no longer fires for DHW only.

CH works fine and the valve on the DHW circuit also operates correctly. I am still able to get hot water by ensuring CH and DHW are set to the same firing schedule.

But if the schedule is DHW only, the valve operates but the boiler does not fire.

Some other information:

Boiler controller always says the DHW demand is off, no matter what.

Connected to an unvented cylinder with a codice dual high limit cutoff thermostat. Thermostat clicks correctly and I have tried pushing the reset button.

On the Navien control centre the thermostat is connected to the "cyl" terminals

My assumption is that somehow the DHW demand signal is no longer triggering (or at least not making it to the boiler). Is there a simple way to test this?

Also, I know I am not qualified to work on an unvented cylinder I am just trying to figure out where the problem lies, if it's the cylinder / thermostat I'll get a plumber in, but if it's something else / simple, maybe I can fix it myself.

Thanks for any advice.

 

[CountryFan]

It’ll be the microswitch not activating on your 2 port valve.

 

[OptimisticDIYer]

Thanks. I did wonder about that.

So the valve has 5 wires, live, neutral, earth, grey and orange. Live neutral and earth are all connected to the relevant connectors but but orange and grey are cut and disconnected. This is by design, the original installer has tapped over the ends of these so I know they have not become disconnected accidentally. I think this might be because the Navien wiring centre connects to the boiler wirelessly? So the switched live from the valve it not needed?

The only connections to the valve are as shown here.

 

[OptimisticDIYer]

Well, it took all day but I figured it out. Don't know how it happened, but the demand control on the boiler was set to thermostat - which I assumed was correct, but it actually needed to be set to"wiring centre". I don't understand how the wiring centre option works, but everything working as expected now. Just heated a tank of water and it switched off at the right temperature.

Maybe this thread is useful to someone else in the future. Thanks for the reply.