Drayton 2 Port Valves - switch driving me nuts

[aesmith]

Our heating has two 2 port valves for heating and hot water, each with a switch that closes when the valve is near to fully open. These switches are in parallel with one side permanent live and the other side signalling to the pump and boiler.

Early last year the switch in the CH actuator started playing up, staying closed when the heating switched off so that the pump and boiler continued to run even though the valve was closed. At the time I replaced the actuator with new, and also replaced the microswitch in the faulty actuator to keep it as spare.
https://www.diynot.com/diy/threads/...e-actuator-faulty-switch.538791/#post-4551863

Now it's playing up again. The fault is intermittent and whenever I test things both actuators work perfectly, so I have only ever "seen" the fault when it's all wired up and live, so I have no way of knowing which of the two is at fault. Since I'd replaced the CH actuator I made a guess and swapped the HW one for the repaired unit, but that hasn't improved things.

Furthermore the fault itself shows itself strangely, with the switch correctly going off when the valve closes, but coming back on again of its own accord sometime later. Not what I'd expect if the switch was sticking. Three times now the system has shut down normally with pump and boiler stopping, only for the system to come on of its own accord once at 03:00 AM and once at 04:45, the third time I switched off the power in the evening after it had shut off on the timer. Then when I switched power back on in the morning the pump/boiler immediately started.

Any ideas on tracking down the issue? I don't really like leaving the system so might run for a long time in that faulty state as it can't be good for either pump or boiler running with both valves closed. However I can't see any alternative to waiting until it goes into that failed state, then investigating and testing live to see which switch is at fault. I say live because based on experience if I remove power the fault immediately clears.

Any comment welcome, Tony S

 

[gas112]

as you know the switch activates when the motor gets power and motors over and the arm presses on the switch and activates it ...once it comes back off and actually turns off just the switch cant then make again without the motor moving over to make this happen so you nust be getting voltage from elsewhere for this to happen...... separate frost stat , built in frost stat faulty timer ...

 

[Harry Bloomfield]

as you know the switch activates when the motor gets power and motors over and the arm presses on the switch and activates it ...once it comes back off and actually turns off just the switch cant then make again without the motor moving over to make this happen so you nust be getting voltage from elsewhere for this to happen...... separate frost stat , built in frost stat faulty timer ...

Once the valve is moved to open, the motor is stalled - the motor is fed with half-wave ac (raw dc), which is enough to hold the position of the motor, but not enough to make it rotate.

Fed up with diagnosing my heating system with a test-meter, I added several a panel of LED lights to the heating joint box, so I could see at a glance what my heating system was up to.

 

[aesmith]

as you know the switch activates when the motor gets power and motors over and the arm presses on the switch and activates it ...once it comes back off and actually turns off just the switch cant then make again without the motor moving over to make this happen so you nust be getting voltage from elsewhere for this to happen...... separate frost stat , built in frost stat faulty timer ...

Thanks, I hadn't thought about frost protection. The boiler is an outside module and I'm trawling through the installation diagrams to try and see whether its frost protection is self contained, or whether it should also operate the circulation pump (which is in the house, not in the module). If it is supposed to run the pump then surely one of the valves should be opened as well, it makes a really horrible noise running with both valves closed, which can't be right.

Two pronged attack, I've asked the installers about expected operation, and I'll see if I can follow the wiring to see what I can learn.

I don't think the days that it ran unexpectedly were particularly cold, but then I don't know what the frost protection is set for.

 

[Harry Bloomfield]

I don't think the days that it ran unexpectedly were particularly cold, but then I don't know what the frost protection is set for.

Usually +5C.

 

[bernardgreen]

I recall changing some micro-switches in CH valves. The switches fitted at manufacture were "economy" versions of an industry standard micro switch. Replacing them with the industry standard micro-switches made the valves operate correctly.

 

[aesmith]

I've ordered a couple of replacement switches from RS, same as I used before.

 

[ianmcd]

if your boiler is outside it should have a frost stat and pipe stat configuration

 

[aesmith]

I had a chance to trace the diagrams for the boiler and it doesn't seem to me that the frost protection stat would (should) trigger the pump. See attached diagram ..

Whether that's exactly how ours is wired up is a different matter of course.

Also attached the internal module wiring, again I can't see how the frost stat would power the pump.

 

[oilhead]

If you have a frost stat, then as the boiler and pump are fired from interconnecting terminals, firing one will fire the other. This is why you have a pipe stat in the circuit so that once the vulnerable pipework is warm enough, both switch off. Obviously if the pump is switched on then a valve must open to enable circulation.

 

[Terrywookfit]

The frost stat and pipe stat are wired in series to energise the Htg valve brown wire which will fire the burner and turn pump on. This overrides the prog and room stat. The pipe stat opens when the return pipe has warmed up

 

[aesmith]

The frost stat and pipe stat are wired in series to energise the Htg valve brown wire which will fire the burner and turn pump on. This overrides the prog and room stat. The pipe stat opens when the return pipe has warmed up

That would make sense but I haven't confirmed that this is how ours is actually configured. However if that's how it's set then it wouldn't cause the issue we're seeing which is the pump running with both valves closed.

There's an alternative configuration noted on the diagram which connects Live and Switched Live inside the boiler, and that configuration doesn't appear to open either valve. I'm not sure if the "CH valve" they refer to is an option in the boiler, or whether they mean the main heating valve in the house.

If fitting pipe stat without fitting CH valve then remove link between 5-6 and connect pipe stat between 5-6

Referring back to the first configuration, I'm not sure I want the whole heating coming on for FP. Would an alternative be an automatic bypass and/or variable speed pump so that it's happy circulating just around the boiler and bypass?

As a temporary measure instead of powering off every night I've been switching the pump to its lowest speed and opened the bypass a little. The "fault" hasn't kicked in since so I don't know if it's any happier like that.

And another question I'm afraid, is this is frost protection for the boiler that I'm seeing, shouldn't it just for a few minutes at a time, not hours on end?

 

[Terrywookfit]

The frost stat puts 240 on T5
The Pipe stat across T5 and T7 supplies the heating valve brown wire (Bypassing Prog and R stat) The valve opens and Puts a supply on T1 which energises Burner and pump.
The pipe stat which is on the return close to boiler, opens when pipe warms up thus removing supply to Htg valve brown, The valve closes and turns off boiler and pump. Simples!!!
This cycle continues until Frost stat is warm enough.

 

[aesmith]

Thanks. Do you happen to know if it's possible to test the frost stat operation so I can see exactly what happens when it kicks in? Save having to trace all the wiring in both boiler and junction box. Because if our installation works the way you say then I need to look for another fault, something which brings on the boiler and pump with both valves closed.

 

[ianmcd]

I have seen frost stats and pipe stats wired to not open the zone valves and circulate via the by-pass, not the correct way to do it, but have seen it done that way, take the tamper cover off aand turn the frost stat up until it operates and you will see what it brings on