Y plan provides hot water when turned off

[Tom5099]

Customer complained of hot water tank getting hot when no demand
Y plan system couldn't see any issues so I watched it
Timer set to CH only, HW off
Thermostat turned to on
Heating comes on as normal, valve moved to CH position
After around 20 minutes the 3 way valve moves to mid point and this is the issue, it then warms the tank when it shouldn't
Can anyone explain why it's calling for heat when it's turned off?
Only thing I can think is does the micro switch in the 3 way valve go faulty causing a false signal to boiler to call for HW maybe? But they would if just open?
Any help would be good please

 

[Tom5099]

Also, the customer said when she went away for a week, the hot water was coming on on its own as she noticed her gas bill was high and the cylinder was warm
Even when the timer was set to off

 

[John.g]

You could turn the HW on at the programmer and then turn down the cylinder stat, the HW "ON" will then feed the diverter valve grey wire via terminal 2 in the stat and might cause the valve to move over again to the CH only position, this will rule out any problem with the orogrammer HW "OFF" contacts or the wiring. You could also remove the actuator and apply a bit of extra torque to the valve shaft in the CH position in case its sticking a little, of course coud also be the internal microswitch.

 

[Tom5099]

You could turn the HW on at the programmer and then turn down the cylinder stat, the HW "ON" will then feed the diverter valve grey wire via terminal 2 in the stat and might cause the valve to move over again to the CH only position, this will rule out any problem with the orogrammer HW "OFF" contacts or the wiring. You could also remove the actuator and apply a bit of extra torque to the valve shaft in the CH position in case its sticking a little, of course coud also be the internal microswitch.

Thank you for the reply
So
Put the timer on CH and HW and then when the tanks hot turn down the temp to 50 degrees and see if the valve moves back to CH only
This would then prove the timer is good

I do have a spare 3 way valve was thinking of changing this but it's a big job if it was something simple that I was missing, I will also check the wiring in the morning but it's only just started she said

What also stumped me was when the heating and HW were both off the HW still came on, it's like something is calling for heat so thought if the micro switch on the hot water side of the valve was sticking, and if that was making that would call for heat from the boiler
Tom

 

[John.g]

If you want to speed things up a bit, maybe switch to CH only first and ensure valve moves fully over, leave like this until (or if) the valve fails to mid position then switch on the HW and immediately turn down the cylinder stat which should force the valve to CH only, you can allways turn the stat back up to 60C (or whatever) and observe the behaviour.

 

[Tom5099]

I am going back within the hour,
CH only and watch the valve, after 20 mins it will fail to mid position and then I'll put HW on also and then turn the cylinder stat

If it goes back to CH only - ?
Or stays in the same place - ?

What would the problem be on these 2 outcomes?

 

[John.g]

If it goes back to CH only after turning down the cylinder stat then suggests fault with the HW OFF contacts or wiring from HW OFF to terminal 7?.
If it stays in the same place then might suggest microswitch fault or sticky valve not going quite fully over to CH only.
Of course chek first that the HW OFF is actually wired to terminal 7., if not it would still work with both CH and HW selected and would still switch to CH only when HW cylinder stat satisfied, I think!.

 

[Tom5099]

Back at the property, wiring all seems fine and in order
Cylinder is cold and sat at 50
It's now stuck on HW only soon as I power it up unless I put CH on and it goes to mid
It's changed from yesterday as I could turn it on and off what ever I wanted
This suspect me to think it's a faulty microswitch, as if it was a wiring fault. It would do the same thing as yesterday every time.
Yesterday I could turn CH on its own but then after a while it would randomly turn HW on

 

[John.g]

Not sure what you mean by "It's now stuck on HW only soon as I power it up unless I put CH on and it goes to mid" If you power it up, HW only selected and cylinder stat calling then it should heat the cylinder until the stat is satisfied and then switch off the boiler and remain where it is, if you then power up the CH and if the cylinder stat is still satisfied it should motor to CH position only, if cylinder stat not satisfied then it should motor to mid position, if CH stat satisfied it should return to the HW position. If CH only selected then it should motor to and remain in this position only. It should allways remain at its last port of call.

 

[Tom5099]

So basically with the timer off on both HW and CH the boiler fired up on hot water only until the cylinder stat was satisfied then it turned off
CH side is fine using the timer and the thermostat they will react as they should

HW, I can basically control the hot water coming on and off with a cylinder stat, even when the timer is set to off
Would this suspect wiring fault or timer issue on the HW off side? Maybe terminals inside or the contacts

 

[John.g]

Something strange there allright, you could remove the wires from the HW ON and HW OFF terminals, then probe both terminals, with HW switched to OFF then there should be 230V on these terminals and 0V on HW ON terminals, with HW switched to ON then 230V on HW ON terminals and 0V on the HW OFF terminals, this should prove the programmer is OK?.

 

[Tom5099]

I will give that a go, do you mean probe the wiring in the control centre on the terminals there
So basically there should be 230v on which ever terminal im asking for
HW on 230v on terminal 6
HW off 230v on terminal 7
If this isn't the case the timers got an issue, if it is the case I'm literally at a dead end

 

[John.g]

You could try it that way but if there is still 23oV at terminal 6 with HW OFF then I would be inclined to probe at the programmer itself with the wire removed from the HW ON terminal, if that switches on/off wirh HW switched on/off then the fault somewhere is.
Here is a schematic of the mid position valve which makes it easier to undersatand, its a very clever device, its shown in the HW position, completely unpowered.

 

[Tom5099]

You could try it that way but if there is still 23oV at terminal 6 with HW OFF then I would be inclined to probe at the programmer itself with the wire removed from the HW ON terminal, if that switches on/off wirh HW switched on/off then the fault somewhere is.
Here is a schematic of the mid position valve which makes it easier to undersatand, its a very clever device, its shown in the HW position, completely unpowered.

John
Thank you for all your help, changed the timer and it's all working perfect
Forum to the rescue again