Firebird Enviromax C20 won't stop heating the Hot Water

[fixit9660]

My Firebird Enviromax C20 is about 5 years old and has been serviced annually. It's run without problem until this morning.
I have it programmed for a daily 20 minute cycle to heat the Hot Water in the Hot Water Tank, 0640hrs - 0700hrs. Today I noticed it was still running an hour later. I checked the EPH R27 Controller and it said, as it should, "Off until tomorrow morning" for Hot Water, and "Off" for Heating. The Wifi Thermostat said it was "Off" too, and to be sure I even turned it right down as far as it would go.
I removed the EPH controller from its wall mount and the boiler still kept going. I only managed to shut it up when I turned off the system at the Mains Isolator switch. I turned it back on a few minutes later and, for now, it's Off, even with the EPH Controller back in place.
Anyone any ideas please?

 

[Terrywookfit]

check zone va;ve.

 

[fixit9660]

I manually operated the Hot Water Valve and at first it didn't "feel" right. It didn't seem to want to operate and/or return well. I've had one apart before and there's not much to them externally. In the past I've had concerns about the cleanliness of the piping; is it possible that muck in the pipe could have fouled the valve and stopped it from closing properly?

 

[Exedon]

If its stuck in the open position boiler/pump will run.
There's a micro switch inside valve feed by a permanent live normally grey wire.
When switch is closed by valve opening a switch live normally orange feeds boiler/pump.
If you have a multimeter and are competent to use it check correct operation in junction box.