central heating won't turn off

[stem]

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.

I would be grateful for an explanation as to what is incorrect in the above please.

 

[D_Hailsham]

Please Read Post 28

 

[D_Hailsham]

I would be grateful for an explanation as to what is incorrect in the above please.

If you read the FAQ I gave a link to, you will see where you are going wrong.

 

[D_Hailsham]

View attachment 150483

This table only takes into account the status of the CH and HW sides of the programmer. The status of the Room and HW thermostats also need to be considered.

 

[stem]

That table was posted as part of a 'Bench Test' using a test rig, that switches a live to the white and grey wires on and off to make sure that the valve was performing as it should. As it's a bench test there aren't any

Room and HW thermostats also need to be considered.

in circuit on a bench test.

If you read the FAQ I gave a link to, you will see where you are going wrong.

I have but I can't see anything incorrect in my statement, my apologies for bring a bit thick.

To help the OP, though, can we agree though that there is a problem with the valve when the white is live (heating required) the grey is live (hot water not required) but the orange isn't live? It should be live as per your diagram below:

I'm out of ideas now anyway, so I'll leave it to you to carry on. Hope it gets sorted.

 

[D_Hailsham]

To help the OP, though, can we agree though that there is a problem with the valve when the white is live (heating required) the grey is live (hot water not required) but the orange isn't live?

In his opening post the OP said:

My problem is that the central heating switches on OK when the programmer goes to a CH on cycle but stays on when the programmer is in a central heating off mode. Something is firing up the boiler when there is no demand. The thermostat appears to work when CH on cycle is operating but has no effect when heating is on when there is no demand from the programmer. The 3 port valve stays in CH position when the programmer has no demand for CH.

So the problem is not No heating when required but Heating when not required.

 

[macwales]

That is correct. Heating stays on when not required. Even with room stat no demand and programmer no timed demand. Only switching off mains supply to programmer and everything else in control system resets 3 port valve to default W position. Without this reset this valve stays in H position and boiler fires up if programmer is switched on even if central heating is in an off period or is set to central heating always off.

Please everybody don't give up on me I still need advice.

Results of more tests with orange wire disconnect

These tests were done in sequence
Cylinder stat always on


P is programmer,
rs is room stat
v is 3 port vale indicator position
b is boiler firing ( yes/ no)
P reset is programmer switched off and then on


P reset
1 CH on, W off, rs off, v W, b no
2 CH on, W off, rs on, v H, b no
3 CH on, W off, rs off, v H, b no
4 CH on W off, rs on, v H, b noh

P reset, rs off, v back to W, b no

5 CH off, W on, rs off, v W, b yes
6 CH off, W on, rs on, v W, b yes
7 CH on, W on, rs off, v W, b yes
8 CH on, W on, rs on, v Mid, b yes
8a CH on, W on, rs off, v W, b yes

P reset, rs off, v W, b no

9 CH off, W off, rs off, v W, b no
10 CH on, W off, rs on, v H, b no
11 CH off, W off, rs off, v H, b no

P Reset rs off valve back to W

12 CH on, W off, rs off, v W, b no
13 CH on, W off, rs on, v H, b no
14 CH off, W off, rs off, v H, b no

P reset returns v to W position


This clearly shows the valve with orange not connected cannot return from position H to W after boiler fires unless power is turned off. When heating and hot water are both on valve is in mid position. When room stat turns off and there is still a cylinder stat demand for heat the valve returns to W position.

With all wires connected and both heating and hot water on, the room stat operates properly and the central heating goes on and off dependant on room temperature as normal. This only occurs when hot water is heating up. When cylinder stat is satisfied the central heating gets stuck on because the 3 port valve does not return to W position when room stat temp is reached. This means that it all works OK until hot water demand from cylinder stat switches off. Thereafter its stuck on central heating on until programmer is switched off from mains power.

I thank everyone for the advice so far and apologise for not making what is happening clear but it has just become clear to me following carry out all the tests you suggested Stem. They were very helpful to my understanding, a special thank you for that.

Question is.... Why is this happening? Please advise me.

 

[D_Hailsham]

This clearly shows the valve with orange not connected cannot return from position H to W after boiler fires unless power is turned off. When heating and hot water are both on valve is in mid position. When room stat turns off and there is still a cylinder stat demand for heat the valve returns to W position.

The result of your tests are all what I would expect; there is nothing unusual about them. The fact that the valve does not return from H to W when the demand for CH ends has nothing to do with the orange wire being disconnected. It is a "feature" of the mid-position valve. The valve stays in H position until either the power is turned off then on, or until there is a call for heat from the HW side.

The 115V you measured on the orange wire when in the "stuck" position is about right (Honeywell say 50V to 150V). I have attached Honeywell's FAQ on the Mid-Position Valve.

The problem is not caused by your valve but by the boiler. For some unknown reason it is lighting when there is only 115V on the switched live. Glow-worm will have the solution. Their Home-owner Technical Support no is: 0344 736 0059. If you had the new components installed by a Gas Safe registered engineer, you should get him to deal with the problem.

 

[stem]

So the problem is not No heating when required but Heating when not required.

Of course. That has never been in doubt, the OP stated it clearly in their first post and several references have also been made to it since.

However, during bench testing of the motorised valve, it revealed that a live on the white wire and grey wire didn't result in a corresponding live on the orange wire, which there should be.

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 still not working correctly.

As you can see above, I explained that I didn't think it was the cause of the problem. However, if those results are correct, the valve actuator is still faulty. I am puzzled why you continue to disagree that there is a fault with the valve. Albeit not the only problem, but a fault non the less.

cannot return from position H to W after boiler fires unless power is turned off

Don't be too concerned about this, it's quite normal, when the heating goes off, if the water is also off, the valve remains in its current position until called for by the hot water. Turning off the power simply replicates a call for HW.

I have tabulated your tests with notes so it's easier for me to follow. Yellow shows when both the programmer and room stat are calling for heat. You don't show what the cylinder thermostat is doing, so I've assumed it's calling for heat as the results suggest. The results are pretty normal, however the problem still seems to be, what we discussed earlier:

Something is firing up the boiler when there is no demand.

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.

Something is telling the boiler to fire when it shouldn't be, it may be the spurious 115V as D Hailsham suggests. I would be interested to know where it is coming from. The heating controls shouldn't be generating it and the results seem to suggest they aren't, So, if the boiler is generating it internally I don't see why it the boiler keep running after the hot water has been operating. Anyway as controls are my thing and I'm not an expert on boiler internals, I leave that bit to the gas safe guys.

I originally asked you disconnect the orange wire only to carry out a specific test, from your post above it seems to be still disconnected.

 

[Hot&Cold]

The 115V you measured on the orange wire when in the "stuck" position is about right

As long as the boiler pcb is correct and the external wiring is correct,Some boilers will fire up with with much lower voltage applied to the switch live. Installing a 0.47 microfarad capacitor fitted between the SL & N on the boiler wiring connection block has been the answer for many worcesters & other gw boilers.

The fault is easily diagnosed whilst on site

 

[D_Hailsham]

However, during bench testing of the motorised valve, it revealed that a live on the white wire and grey wire didn't result in a corresponding live on the orange wire, which there should be.

If that is correct, how is the boiler lighting when CH only is called?

I would need more details as to how the "bench test" was carried out before commenting further.

As to the source of the spurious 115V, read the Honeywell FAQ.

Note 4 is not correct; the valve does not remain in mid-position when CH goes off. When the valve is in mid-position, both CH and HW must be calling for heat. If CH stops calling, there is no voltage on the white wire, so the valve is no longer held in mid-position by R1 and the diode. The vlave therfore returns to the HW position. If HW stops calling, the grey wire becomes live, via programmer or HW stat, so the valve moves to the CH position. It's only when the valve is in CH position and the call for heat stops that the valve remains in the CH position and 115v appears on the orange wire.

 

[Hot&Cold]

[QUOTE edited as not helpful

 

[Hot&Cold]

Bench testing and on site testing will vary,the fault is easily rectified. Maybe cost around £160 + vat for a permanent repair.

Doubt it is diy work

 

[stem]

To clarify D Hailsham question re: testing of motorised valve.

Results from the OP. Bench test with the valve wired to two switches that provide lives to white and grey wires, and with multimeter on orange wire. Result when both white and grey wires are live, no output on Orange wire.

I have made a two switch test rig

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

Test results of valve when wired into the heating system, shows 115V has appeared.

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

Hope this helps.

 

[D_Hailsham]

To clarify D Hailsham question re: testing of motorised valve.

Results from the OP. Bench test with the valve wired to two switches that provide lives to white and grey wires, and with multimeter on orange wire. Result when both white and grey wires are live, no output on Orange wire.

Test results of valve when wired into the heating system, shows 115V has appeared.

I read about the two switches and the strange result it gave when "bench tested", which contradicts the result when "wired into the heating system", and thought - that's not right. Then I thought - How exactly is he carrying out the bench test? Is the valve still plumbed in? Or has it been removed completely? Or has just the actuator been removed? Only the OP can answer that question, so please don't speculate.