Hot water on when off at programmer

[Bobthebuilder95]

Hi all,

Recently had boiler fixed, new fan, in our new house. Tonight I noticed it was very hot even with thermostat down low, checked and the boiler was still on. This is with the heating set to on but hot water off.

I then went up to the hot water tank and turned the tank stat down to minimum. This then clicked off the boiler. With the boiler then off turning the wall thermostat up and down clicked the boiler on and off as it should do.

So my question is why is the hot water still on when turned off at the controller and why does the hot water thermostat effect of the heating is on?

 

[Madrab]

If you have a hot water cylinder and 2 port valves? I'd be looking at the valves first.

Get the chap back that replaced the fan to have a look.

 

[CBW]

Agree with @Madrab, sounds like a 2port valve failure.

 

[Bobthebuilder95]

Hi everyone. I have done some more investigating tonight. And the 3 port valve is moving to all 3 positions as it should. However it is doing so with only the hot water turned on.

That is to say with the heating set to off at the control panel but the hot water on the three port valve will act as if the heating is turned to on and supply heating. If hot water and heater are both set to off then neither are on as it should be.

Also with the heating on it stays on full blast and won't adjust based on the thermostat depspite the wireless thermostat relay clicking on and off as it should.

Any ideas?

 

[stem]

This sounds more like incorrect wiring to me than the failure of a component. For a start, the cylinder thermostat shouldn't even have a live supply to it when the programmer is at 'Hot Water off' so there is no way that it should still be controlling the boiler.

Has it ever worked properly? Has anything else apart from the fan been changed or disturbed? New smart thermostat or programmer fitted recently for example.

 

[Bobthebuilder95]

Hi, one more evening spent and getting closer hopefully!

I have now compounded the issue where if the hot water is set to off and the cylinder thermostat turned right down the heating will work exactly as it should. However witj the cylinder thermostat up at 60*c this will cause the heating to run continuously irrespective of room temperature. Any ideas?!

 

[stem]

HW ‘off’ at programmer will supply voltage to ‘satisfied’ terminal of cylinder stat.

Exactly. But where does the live that the cylinder thermostat should be switching to the 'satisfied' terminal come from?

It comes into the 'com' terminal of the cylinder thermostat from the programmer which is (or should be) off.

Which is why I believe that the wiring is wrong. Its the other terminal (Call) that is responsible for controlling the boiler, and it is never electrically connected to 'satisfied' [Where HW off from the programmer should be connected] under any conditions.

 

[fezster]

HW ‘off’ at programmer will supply voltage to ‘satisfied’ terminal of cylinder stat.

More importantly, "HW off" from programmer supplies voltage to the grey wire - this combined with live on the white wire from the room stat, means the 3 port valve would be in "heating only" mode.

OP says that with HW off, but cylinder thermostat set high (and room stat is off), the boiler fires and he gets heating only. I suspect the cylinder thermostat is wired in place of the room stat into the white terminal of the 3 port valve.

 

[stem]

Interesting. Initially I thought that, then discounted it because it doesn't explain the rogue live supply to the cylinder thermostat when the hot water should be off.

Unless as well as the cylinder thermostat 'call' being connected to the motorised valves white wire. The cylinder thermostat gets its supply on 'Com' from the 'heating on' and not 'hot water on' at the programmer as well.

Methinks there has been some tinkering going on and the OP's not coming clean

 

[fezster]

I think you may be right. OP, if you're handy with a multimeter, you should be able to diagnose this yourself. Google "Y Plan" heating system to see how it should work and go from there.

Otherwise, you need a heating engineer to check the wiring for you.

 

[stem]

I think the cause of the spurious live supply to the cylinder thermostat may now have been found. The OP's got another thread going about it here.