ST6300a timer failed?? Or is it the 3way valve??

[tgs166507]

Hi.
I have an st6300a timer switch and have noticed that the central heating is ticking on for a second or two every say 10 seconds even when both the hw and ch are set to off.
I have also noticed that the Honeywell three way valve is not sealing, in that over the summer when I've had the ch switched off, some of the upstairs radiators have been getting warm when the hw is running.
Is this likely to be a failed timer unit? Or is the timer being messed about by a failed valve?
Thank you in advance for your assistance.

 

[D_Hailsham]

Are these new problems, i.e the system used to work correctly?

 

[tgs166507]

I can't categorically say that they're new, but I am fairly confident that they are new issues. Certainly the timer ticking on and off...

 

[D_Hailsham]

I have also noticed that the Honeywell three way valve is not sealing, in that over the summer when I've had the ch switched off, some of the upstairs radiators have been getting warm when the hw is running.

Does the pipe from the 3-way valve to the radiators feel hot when the CH is off? Check at least 30cm (1ft) away, so you don't get any transfer vial the metalwork.

If yes, the valve is passing; if no, you have reverse circulation. Water is circulating the wrong way round the heating system. This is caused by the returns for the heating and hot water cylinder connected in the wrong order.

the central heating is ticking on for a second or two every say 10 seconds even when both the hw and ch are set to off.

Turn off the power to the system (CH and HW off at the programmer is not enough); wait a few minutes; turn back on.

Does the problem go away?

 

[tgs166507]

Thanks for taking the time to reply.
The timer issue seems intermittent if I'm honest.
What I have done though is electrically isolate and remove the power head. How much movement should there be on the spindle? You can barely move it with fingers, and with an adjustable spanner on it, it only moves slightly, say by 1/16 of a turn?
I expected that it would turn more than this??
Thank you

 

[D_Hailsham]

How much movement should there be on the spindle? You can barely move it with fingers, and with an adjustable spanner on it, it only moves slightly, say by 1/16 of a turn?

The valve spindle should turn easily by hand; 1/16 turn is about right.

If you need a spanner to turn the spindle the valve is sticking, which could account for your problems. Try lubricating the spindle with silicon lubricant (WD 40 etc will rot the seals).

If that doesn't work you will need a new valve. However if you have a Honeywell you can buy a repair kit consisting of the top plate, spindle, etc.

 

[tgs166507]

A bit more investigation.
The valve will move from HW port b to CH port as required.
It is very reluctant to move the other way from CH back to mid or HW.
With HW and CH both calling, I get 240v on both white and orange until the valve reaches mid travel at which point the voltage drops to 170v. There is zero on grey.
With HW only, I get 240v on orange and zero on white and grey .
With CH only, I get no power anywhere.

At no point have I measured power on grey.

Does this shed any light?
Thanks.

 

[D_Hailsham]

The valve will move from HW port b to CH port as required.
It is very reluctant to move the other way from CH back to mid or HW.

How did you check this?

With HW and CH both calling, I get 240v on both white and orange until the valve reaches mid travel at which point the voltage drops to 170v. There is zero on grey.

Do you mean the voltage on white and orange drops to 170?

With HW only, I get 240v on orange and zero on white and grey.

That's correct. The valve is not in circuit for HW only.

With CH only, I get no power anywhere.

There should be 240V on white and grey (and on the orange). This comes frm the CH thermostat (white), and the HW thermostat or Programmer HW OFF (grey). So you need to check that.

 

[tgs166507]

To test the movement I set the programmer to CH only and watched the valve move across. I then set it to hw only and the valve very slowly crept back or stopped, and required assistance with a screwdriver pressing on the spring return lever to reach its full travel.
You are correct that the voltage drops from 240 to 170 when it reaches mid travel whilst moving from CH only to hw and CH together.
I checked the wiring on CH only and I still get no voltage between neutral (blue) and any of the wires. I do however get 240 between the neutral and the motor cover and the motorhead cover which I found a little odd.

 

[tgs166507]

At the risk of looking stupid I have repeated the voltage measurements to earth (rather than to neutral).
CH only gives 240 on white, orange and grey.
Ch and HW gives 240 on white and orange, and 80 on grey.
HW only gives 240 on orange and zero on white and grey.

When I switched the ch off on the programmer I observed it ticking on and off again. This seemed to be when the valve doesn't travel across from mid to HW only position, and stopped once I had 'assisted' the valve to travel across.

Does any of this make any sense?

Thanks for your help. I'm very grateful.

 

[D_Hailsham]

Have you removed the actuator and checked the spindle turns easily by hand?

Which make valve do you have?

The voltage disrepancies using earth/neutral suggest a wiring problem somewhere. Make sure all terminals in the junction box etc are done up tight.

There are detailed fault finding instructions for mid-position valves in the CH Faq section.

 

[tgs166507]

I have taken the whole motor head off and the spindle will turn by hand, but not particularly easily.
The valve is a Honeywell v4079.
It appears like the spring effort is not enough to pull the valve back towards the hw only position.

 

[D_Hailsham]

I have taken the whole motor head off and the spindle will turn by hand, but not particularly easily.
The valve is a Honeywell v4079.

It should turn very easily. It could be the stiffness which is causing the problem. Try lubricating with silicon lubricant.

I think you mean V4073!

 

[tgs166507]

Thanks. I tried silicone lube last night and no real improvement.
It looks like surgery is coming up...

 

[D_Hailsham]

Thanks. I tried silicone lube last night and no real improvement.
It looks like surgery is coming up...

You can get a replacement ball and 'O' ring kit; part no 272742A for about £8.