Heating wont turn off

History:
Open vented Y plan system originally had a problem where CH could not be obtained. Doing the CH two wire test on the 3 port valve, showed that this was at fault. Replaced the 3 port valve with a Honeywell 4073 one at the weekend. I am an electronics tech, and also took a photo of the wiring before I swapped the valve over - I swapped one wire at a time and am confident I have not introduced a wiring problem.

The situation now is that on some occasions the CH is not tripping off. Even turning everything off at the programmer does not stop the pump/boiler running. I started to fault find but didnt get very far. What I noticed was that with the fault condition present, and the 3 port valve full over to supply CH (which I think would be the normal place for it to be if just CH had been called and was then satisfied), the orange wire was not live - so presumably the cylinder stat was feeding a live to the pump and boiler. Sometimes (but not always) switching the heating off at the programmer can switch the CH off, but the symptoms are not yet forming a reliable pattern. I should add that the boiler does trip itself out from time to time, presumably when it is internally at it max temperature, but then fires up when it cools a bit.

Any ideas please chaps. Which components can I rule in or out. What simple checks can I do.

Thanks.

First thing to do is get a wiring diagram for your particular boiler and valve(s), and verify that it is all wired up as should.

what is the "2 wire test"?

from No 17 in the FAQ


"CH Only Test (Port A open)

Turn Power OFF at main connection for the system (turning CH and HW OFF at programmer is not sufficient) This resets the valve to rest position
Disconnect white valve wire from terminal T5 and grey wire from terminal T7.
Connect white and grey wires to permanent Live (T1)
Turn Power ON
Valve should move over so port A is open and boiler light (check by feeling that only the pipe from port A gets hot)

If the valve does not move, Switch S1 is not moving over.
If the valve moves but the boiler does not light, switch S2 is not moving over. (check 240V on orange)"

OK, I have never read through the FAQs.
What do you mean by "tripping" is it shutting down as it should or locking out and needing a reset?
the orange wire not being live when the CH is calling for heat would usually mean a wiring fault - as you have a new valve.

Yes sorry, poor terminology, the boiler is NOT "tripping" as in needing a reset, it just stops for a short period every now and then and fires back up. It used to do this when it was all working OK, so I assume it is normal. I mentioned it in case my description of running continuously was taken literally. The point I was trying to get at is that it can run even though the programmer is off.

I am still gathering symptoms, but I am becoming convinced that the CH does switch off if the water is being called for, but runs continuously if the water has reached temperature.

check the white and grey have not been swapped over. there should be 2 cores connected to the grey, only 1 to the white (assuming all the components are wired straight back to the wiring centre)

Yes grey has two wires, white has one.

I have been checking the wiring out in the airing cupboard and it seems fine, I now need to run some checks down to the room stat down stairs and across to the programmer - these are more difficult to do as the wiring is concealed.

One thing I have noticed is that the CH does not come on until it is called for, but then does not turn off after it reaches its temperature. I.e. after a reset of the system the CH will come on if I turn the room stat up. However, once running it will not turn off if I turn it down. In this condition (with the HW stat turned right down) I believe have 240v on HW OFF, 240v on HW ON (this feeds back from HW OFF through the HW stat I assume) and 240 on CH lines in the airing cupboard.

I would assume that this would be a faulty stat, except that turning the programmer CH off does not turn the CH off either.

Thoughts please - where to look next ?

Just carried out another check. With system turned off, and both stats turned down I turned the system on and turned the room stat up - boiler fires up /pump runs - CH is running. Turn the room stat down CH continues to run.

Checked the voltage on the white wire where it joins the feed from the room stat =240VAC. I then removed the white wire from its connector to the roomstat, and the room stat connector feed drops to 0v. I checked the white wire which is hanging loose and not connected to anything, it is showing 240VAC. Orange and grey are also 240v, so I remove the orange wire from the feed to the boiler/pump and the white wire still shows 240V.

I need to check this yet but does this mean that SW1 is short circuit and the white is feeding from the grey internally in the 3 port valve? Or, are there any normal use circumstances where it is possible to get a live white wire FROM the 3 port valve.

I reckon you have miswired the connections to the valve, follow the inputs/outputs on the link,

http://www.octaveblue.co.uk/c_heating/

That's a great reference diagram, thanks.

The wiring (sadly) appears to be OK. This is a photo I took before I started making any changes, and the system was fitted in a new build and worked properly like this - and it matches up the same now after fitting the valve. I note that the order of the connections on the chocolate block differs from the diagram given above, but the physical connections are the same.

//www.diynot.com/network/MartyMalabu/albums/8578/34118

However, these are the voltages I am seeing as I step through from full reset, HW only, HW+CH, CH only, Neither. I am calling for both at the programmer, but turning each off as necessary using the thermostats. Sorry about the presentation, I had problems with the tabbing and alignment. I hope it makes sense. All voltages AC.


___________Reset____HW___Both__CH___Neither

White_______0v______0v___240v__240v__240
Grey_______240v____56v___65v___240v__240
Orange_____50v_____240v__240v__240v__240
Pump/Boiler_Off______ON___ON____ON___ON
Port Position_B_______B_____MID___A____A


I think this is OK, until the last step (Neither) when I would expect the White & Orange to be 0v and the Pump/Boiler to turn off. However the pump/Boiler just keeps on going regardless, and the White and Orange are live. It follows that if White is live then Orange and Pump/Boiler will get live too - so perhaps this is the nub of the problem ? Why is White live in this state ?

[Edit : Just realsied the Orange is Live for HW only. This confused me - but this is correct as this is feeding 240v from the cylinder stat in parallel with and onto the orange wire - so this is OK I think]

As the sequence works OK until up until the last step, does this look like my new 3 port valve may be faulty

Any ideas please guys ? Next steps ?

MartyMalabu said:

Just realised the Orange is Live for HW only. This confused me - but this is correct as this is feeding 240v from the cylinder stat in parallel with and onto the orange wire - so this is OK I think

Click to expand...

This can be confusing as the boiler can be fed from two places: the HW cylinder stat or the valve orange wire. When HW is involved (HW only, or HW with CH) the boiler is fed from the cylinder stat. When CH only is running, the orange wire supplies voltage to the boiler.

Run through all the tests in FAQ 17 in sequence and you should be able to identify the cause of your problem.

Thanks for your post D.H.

I ran through all the tests in sequence. All tests behaved normally apart from the following anomolies :

In test 3 (CH & HW) the implication in the step to turning the cylinder stat up, is that this action should trigger the boiler to light. However the boiler lit anyway as soon as I powered on, even with the cylinder stat turned down. I checked the orange wire at that point after temporarily disconnecting it from the connector, and it was showing 220v. That did not seem right (although the test did not say that the boiler should not light at that point, I suspect this is a fault).

In test 3 (CH & HW), with HW already off, turning the CH off, did NOT turn the boiler off, and the orange cable showed 220v.

Your test schedule indicates that the new actuator is duff - would you agree? I have ordered another head unit and hope to fit it soon.

Thanks again.

MartyMalabu said:

I ran through all the tests in sequence.

Click to expand...

Did you check if the valve was sticking and that the wiring is correct before carrying out the tests?

In test 3 (CH & HW) the implication in the step to turning the cylinder stat up, is that this action should trigger the boiler to light.

Click to expand...

Correct. In the CH+HW situation the boiler is controlled by the HW thermostat. There should be no voltage on the orange if it is disconnected.

In test 3 (CH & HW), with HW already off, turning the CH off, did NOT turn the boiler off, and the orange cable showed 220v.

Click to expand...

Another possibility is the valve sticking.

When in the fault condition (boiler running when CH and HW are both off), check the lever in the MAN/AUTO slot. You should get resistance as you move it from AUTO to MAN as it is opening the valve against a spring.

If you find that the lever is very loose in the slot, either the valve is sticking or something external is holding the valve in the CH only position.

Check all wiring carefully (loose strands touching adjacent terminals etc).

When in the fault condition (boiler running when CH and HW are both off), check voltage on White. (The grey should have 230V from the HW stat "sat" terminal or from the programmer HW OFF terminal.)

If there is 240V on white (it should be 0V) check back to CH stat and programmer CH ON terminals for the source.

Only when you have eliminated everything else should you suspect the actuator.

I have fitted a new actuator and we can now rule that out as the boiler continues on with both thermostats turned down.

I am pretty certain the valve is not sticking - and in any case it is only a week old.

When in the fault condition with both stats turned down the manu/auto lever is loose. This is because the motor had previously been at the CH position and is still receiving power since turning the stats down - so is still in that position.

In the fault condition there is 240v on both grey and white (and orange). I disconnected the room stat feed where it meets the white and it is 0v, so the 240v is feeding out on the white from the actuator - obviously derived somehow from the grey wire. If I disconnect the grey wire at this point the motor returns with the spring to its rest position and the orange and white drop to 0v and stay there after I have reconnected the grey.

While checking the problem with the new actuator I have observed a slight change in symptoms. I can now turn the heating off if I do it at the programmer, but if I try this by turning the room stat down it has no such effect - the boiler runs on. I noticed that if I twist the programmer slightly that the HW light comes on. I am now wondering if my problem is the programmer. Could the programmer be causing these symptoms due to a flakey connection (perhaps leaking the NOT HW signal onto the CH signal).

Or is this unlikely? The unit is a Honeywell ST600C. How reliable are these, it is about 9 years old.

Many thanks for your time.