central heating won't turn off

[macwales]

Sorry for the confusion.

I should have said 'the new 3 port valve and actuator was carefully wired to the same terminals in wiring centre as the old one'

I was trying to make it clear that the new 3 port valve fitted is the present snap on actuator type while the old one had the actuator screwed to the brass valve body.

 

[stem]

So from your results:

White wire 3 port valve at H with no programmer demand 0 (zero) volts

This voltage on the white wire is what it should be. Without heating demand, there should not be any voltage applied from the heating controls to the motorised valve to open the heating port. But as you say, it is open!

Orange wire 3 port valve stuck on H with no programmer demand 115v

That's a bit high. This is the wire that provides the live from the motorised valve to run the boiler, and should ideally be quite a low figure when neither a heating or hot water demand is present. Voltages do appear and they vary from system to system, probably because of being fed back via the boiler's circuitry. Based on that, I tend to agree with the post from D Hailsham:

if you have a multimeter (and know how to use it), check the voltage on the orange wire when CH is On (240Vac) and Off (50-150Vac). If the Off voltage is higher than 150Vac the problem could be the valve. If below 150Vac, the boiler is probably the problem.

Once the valve has moved to the heating only position, the orange and white wires are connected by a switch inside the motorised valve. I suspected that some voltage from the boiler is fed back via the orange wire and through the switch was sufficient to keep the valve open. BUT, the bit I can't get my head around, is that if that was the case, the white wire which is now connected to it would also be at 115V and it isn't. So, I'm tending to think that it may be the valve.

Personally, my next step would be to 'bench test' the motorised valve actuator. If you are competent and can do it safely, it's not too difficult. I have a little test rig with a switch for each of the inputs (White and Grey wires) and connect my multimeter to the orange wire to show when it's 'on'. By switching the white and grey wires on and off, it's easy to check that the valve position and the output from the orange wire are as they should be according to the table below:

Your other results below look more or less OK, I don't see anything obvious:

Orange wire 3 port valve at H with CH programmer demand 115v

That's low if the room thermostat was also calling for heat. But it's not low if it wasn't, in which case would expect to see the same voltage as the previous result (115V)

Orange wire with 3 port valve at mid position with demand from programmer for hot water and CH 250v

That's as expected as the HW cylinder thermostat will be providing it from the hot water control side.

White wire with 3 port valve at mid position with demand from programmer for hot water and CH 250v

That's as it should be, same as above. White and orange wires now connected via internal microswitch.

 

[macwales]

Thank you for all your effort. I will carry out the test you suggest on the new actuator. It will take me some time.

I originally thought the brass valve was stiff and have worked if by hand a few times. It moves but is not loose but I have nothing to compare it with so have ordered another (valve body only).

With actuator snapped onto brass valve body, it is sticking after CH has been on and programmer turns CH off and is then stuck in Heating position on actuator indicator. It returns immediately to hot water position when the power to the programmer is turned off so the springs must be able to return it. Could it be a stuck microswitch in the actuator?

This action of turning the power to the programmer off turns off power to the boiler as well on my system.

The boiler has an overun that makes all observations take some time.


Boiler is in garage.
Programmer in downstairs utility.
Room stat in downstairs hall.
Wiring centre and 3 port valve are in airing cupboard upstairs with cylinder stat on hot water tank.

 

[stem]

This is a bit off an odd one. Originally I thought of 3 possibilities but there is one different result / symptom for each that has led me to rule each one out. I explained one of them in my last post.

I agree that something is keeping the valve open. I considered a stuck microswitch, but the live that opens the heating port is applied to the white wire from the controls, and as you have tested it is 0V when the programmer is off, if the microswitch was faulty and sticking 'on' then the same voltage would appear on the white and orange when in the heating position, but it doesn't. If it was sticking 'off' then the boiler wouldn't come on when only the heating 'on' was selected.

It's difficult to fault find over a forum without being able to examine everything.

Perhaps a simpler test I would try, is to disconnect the orange wire and operate the system now. The boiler shouldn't actually fire up the central heating with the orange wire disconnected (it should still work with the hot water though) If the fault is still present (ie, the valve still sticks in the heating position with the programmer off) you can rule out the boiler causing the fault, because it isn't connected to the boiler anymore.

 

[macwales]

I have made a two switch test rig which I have left connected for now.

I ran the test through several times. It was carried out with central heating only at programmer and room stat on high.

Results differ from your table

white off grey off valve is in W position 0v on orange wire

white on grey off valve is in mid position 8.9v on orange wire

white off grey on valve is in W position (has moved) 0v on orange wire

White on grey on valve is in H position slight voltage 0.1v on orange wire

 

[stem]

I have made a two switch test rig.

That was quick!

I ran the test through several times. It was carried out with central heating only at programmer and room stat on high.

OK, but when I said:

my next step would be to 'bench test'

A 'bench test' means that the valve is being tested on a bench. ie out of the system and so not connected to the programmer and room stat anymore.

EDIT: Regarding the tests.

white off grey off valve is in W position 0v on orange wire

That's OK as per first line of the table.

white on grey off valve is in mid position 8.9v on orange wire

Also OK as per second line of the table

white off grey on valve is in W position (has moved) 0v on orange wire

This could be OK. The valve "stays in last position" with his test, so if there has been a slight delay in moving from test 2 to 3 that has allowed the spring to move it back towards the W position that's OK.

White on grey on valve is in H position slight voltage 0.1v on orange wire

That's right in that the valve is in the H position, But, the orange should read 230V

 

[macwales]

We are getting crossover on our messages so I will wait to hear from you about the test results on the table you provided before doing the disconnected orange wire test.

By the way, the new 3 port valve body has arrived and the spindle is nice and loose but then there is no water in it so no friction.

I will have to fit this new valve body if I am to take a faulty valve and actuator back to Screwfix for a swop.

 

[stem]

I have edited my earlier post to show comments about the test results. The only really wrong one is the last one, but I can't figure out how that would cause the problem you describe.

Also, I don't think the valve is sticking as it returns freely to W when you power down everything.

 

[macwales]

Thank you for bearing with me it is much appreciated.

I have disconnected and isolated the orange wire to the 3 port valve.

Test results now

CH on at programmer, room stat on high, water at programmer off, 3port valve at position H, boiler NOT firiing.

CH & W on at programmer, room and cylinder stats on, 3port valve at position mid, boiler firing and radiators warming.

CH off & W on at programmer, room and cylinder stats on, 3 port valve at position W, boiler firing but I think radiators were cooling from test directly above, so central heating not on.

I have reconnected the orange wire to the wiring centre and performance is as before with same fault ie. Water working Ok but CH sticking on when room stat and / or programmer says it should be off.

So do you think there is a chance that I have been sold a faulty actuator? Or is it the house wiring?

 

[stem]

OK, based on that:

CH on at programmer, room stat on high, water at programmer off, 3port valve at position H, boiler firing.

Interesting! That's the wrong result. With the orange wire disconnected and only the heating 'on' the valve should move to H as it has, but the boiler should not be firing (because it's the orange wire that does that) This will need investigation to find out where the boiler is still being energised from.

A bit of a long shot, but is there a frost thermostat anywhere? I say long shot, because 1) it shouldn't operate until there's a risk of freezing, and 2) A frost thermostat should be wired to the motorised valve not the boiler.

CH & W on at programmer, room and cylinder stats on, 3port valve at position mid, boiler firing and radiators warming.

That's as I would expect. In mid and W positions the hot water cylinder thermostat controls the boiler not the motorised valve, so that's OK

CH off & W on at programmer, room and cylinder stats on, 3 port valve at position W, boiler firing but I think radiators were cooling from test directly above, so central heating not on.

Also OK.

So do you think there is a chance that I have been sold a faulty actuator? Or is it the house wiring?

Based on the first result above I am leaning towards a wiring fault. In the bench test the actuator seemed to perform OK, except for the lack of 230V on the orange in the H position. Maybe there is more than one fault.

 

[macwales]

My sincere apologies, I must have deleted the word 'not' or I typed it wrong and at the the most important bit. I have edited post no 24 above so it is now correct.

It should be

Orange wire disconnected

CH on at programmer, room stat on high, water at programmer off, 3 port valve at position H, boiler NOT firing.

 

[macwales]

About the frost thermostat.

I believe the Glow-Worm boiler has an internal frost stat. There is another external one in the boiler supply feed next to a three pole isolator switch. The isolator switch and external frost stat are both in the garage beside the boiler. The switch wire in the external frost stat is disconnected and isolated. It has been this way for years during which the heating has been working fine. When the condensing boiler was fitted 5 years ago the frost stat housing box was wired internally just as a junction box connecting only the boiler power feeds L and N and Earth wires. I have checked that this is the case.

If the internal boiler frost stat switch was faulty and activated , powering off the programmer would surely not reset it.


To sum everything up.

Now I have corrected my stupid mistake the orange wire disconnected test indicates everything OK with the boiler.

But the table you provided test with white wire on and grey wire on showed 3 port valve position H which is correct but near zero voltage on orange wire which is incorrect as it should be 230v.

So if my logic is correct then the absence of this 240v is significant as it is the only thing that seems out of place

What does this mean?

 

[D_Hailsham]

Results of voltage tests

White wire 3 port valve at H with no programmer demand 0 (zero) volts

Orange wire 3 port valve at H with CH programmer demand 115v

Orange wire 3 port valve stuck on H with no programmer demand 115v

Those voltages are what I would expect. The pics below show the four possible conditions for a mid-position valve. You will see that when CH only is satisfied there is a path from the programmer HW OFF or HW stat SAT terminal through R2 to the orange wire and consequently to the boiler. The value of R2 is normally sufficient to reduce the voltage so the boiler does not fire. 115 Volts should be low enough, so the problem must be in the boiler.

[GALLERY=media, 31085][/GALLERY][GALLERY=media, 31084][/GALLERY]

Orange wire with 3 port valve at mid position with demand from programmer for hot water and CH 250v

When in mid position and there is a demand, the boiler is controlled by the wire from cylinder stat call valve. This wire and the orange wire both connect to the same terminal as the switched live to the boiler So the 250V actually comes from the HW stat not the orange wire.

 

[stem]

OK thanks, like I said, the frost stat was a long shot, but I'm running out of ideas.

Now I have corrected my stupid mistake the orange wire disconnected test indicates everything OK with the boiler.

So, from this I assume that when you tested it with the orange wire disconnected the valve positioned itself as it should and didn't stay in H when the programmer went off, and the boiler didn't fire. Is that correct?

But the table you provided test with white wire on and grey wire on showed 3 port valve position H which is correct but near zero voltage on orange wire which is incorrect as it should be 230v.

So if my logic is correct then the absence of this 240v is significant as it is the only thing that seems out of place

What does this mean?

That's a good question. The absence of the 230V on the orange wire when the valve is in H position (white and grey live) should mean that the boiler wouldn't come on when the valve was in the H position, when in reality the opposite is true....which is really baffling... Anyway, if the 230V is missing, under these circumstances, the valve is certainly not working correctly.

 

[D_Hailsham]

Then I suspect, that possibly they haven't been wired in correctly. Why were they changed? Was there a fault before, and if so what was it? You are quite right when you say:


When unpowered, the motorised valve is held by a spring to close the central heating outlet.

When central heating is required, the motorised valve receives power (on its white wire) from the room thermostat via the programmer to operate the motorised valve motor and open the heating outlet.

If the thermostat, or programmer go 'off', the live should be lost and the spring pulls the valve back to close off the heating port.

It's possible, if it's been wired in wrongly that there is still a live on the white wire when there shouldn't be. Someone with electrical knowledge and a multimeter would be able to physically check this.

That's only partly correct.

I suggest you read Mid Position Valve Explanation