Boiler puzzle

luke-warmwater · 17 Feb 2015

Hi,

I'm having a confusing time with my central heating and wondered if anyone can suggest what the cause of the problem might be?

We have a Glow-worm Ultracom 30hxi boiler which provides CH and HW. Tanks in the loft and HW cylinder in landing cupboard. Boiler fitted 2009.

Here's the problem...After the central heating comes on it only runs for about 5 or 10 minutes and then goes off and stays off. However if I go to the thermostat in the hallway and turn the dial DOWN until I hear the faint click and then turn it straight back UP again to 20 degrees, the boiler restarts and then keeps running as normal.

There are no error codes showing on the boiler and no weird noises.

The same thing happens every time, not randomly.

Is it a faulty room thermostat? When I turn the dial I can hear the'click' although its very faint. If I set the thermo very low, the boiler stays off. Hot water seems ok.

Anyone had this before?

D_Hailsham · 17 Feb 2015

Which type of motorized valve do you have?

View media item 5946 View media item 11762

luke-warmwater · 17 Feb 2015

Thanks for your reply. Sorry, I dont know what type of motorized valve I have.

Sounds like you think that might be the culprit?

luke-warmwater · 17 Feb 2015

Ah...OK, I've located the motorized valve and it is a Honeywell.

I can't see any model number on the outside but I've taken the cover off and can see markings that read Synchron 8734.

muggles · 17 Feb 2015

Back up a bit and look at the pictures - one has two connections and one has the connections. Which one looks like yours?

luke-warmwater · 17 Feb 2015

Its a 2 port.

I have 2 of them in the airing cupboard. I have given them a little test by gently pushing the lever across (system off). They both present smooth resistance after the first couple of mm and then self-return to the starting position ok.

D_Hailsham · 17 Feb 2015

luke-warmwater said:
It's a 2 port.

Not so hard as you first made out.

I have 2 of them in the airing cupboard. I have given them a little test by gently pushing the lever across (system off). They both present smooth resistance after the first couple of mm and then self-return to the starting position ok.

That's what should happen.

One valve will be in the branch to cylinder and controls the hot water; the other is in the branch to the radiators. It's the radiator one we are interested in.

Turn the heating on, so it is running.

Now try moving the lever of the CH valve across.

You should find it is very loose and doesn't return to the right when released.

Wait for the fault to occur. Then check the lever again.

Is it loose or providing resistance?

luke-warmwater · 17 Feb 2015

Firstly, thank you both for taking the time to reply and for your interest in my problem

Now I know a bit more about what a motorized valve looks like, I've followed your instructions. With the system running, the lever on the CH valve is loose as you said it should be.

After about 10 mins the usual fault occured and the boiler stopped running. As you suggested, I tried the lever after the fault occured and it is still loose and does not return to the starting position. Hopefully that tells us something?

In order to be thorough and to give you all the available info, I then went to the thermostat in the hallway and turned it down to zero. The thermo made the usual faint click and a bit of a mumble from the boiler which stayed off. I checked the lever on the CH valve again and now it had returned to offering resistance. After a couple of minutes I turned the thermo back to 20 degress, the boiler fired up and the CH valve lever went loose again.

Once I've been through this ritual of waiting for the error, turning the thermostat down and then back up again, the boiler runs as normal. Happens every time.

Again, I greatly appreciate your input and hope that the above description is clear enough for you to throw further light on the cause.

Thanks, Luke.[/u]

D_Hailsham · 17 Feb 2015

luke-warmwater said:
With the system running, the lever on the CH valve is loose as you said it should be.

Good.

As you suggested, I tried the lever after the fault occurred and it is still loose and does not return to the starting position.

That means the thermostat is holding the valve open. The microswitch in the valve should be closed so the boiler should still run.

I then went to the thermostat in the hallway and turned it down to zero. The thermo made the usual faint click and a bit of a mumble from the boiler which stayed off. I checked the lever on the CH valve again and now it had returned to offering resistance.

That proves the room stat is working correctly.

After a couple of minutes I turned the thermo back to 20 degrees, the boiler fired up and the CH valve lever went loose again.

OK

Once I've been through this ritual of waiting for the error, turning the thermostat down and then back up again, the boiler runs as normal.

The problem is either a faulty microswitch in the valve or the boiler has a fault.

Do you have a multimeter and know how to use it?

luke-warmwater · 17 Feb 2015

Thanks again for your reply.

No, I'm afraid I dont have a multimeter, but I could get one and learn how to use it.

luke-warmwater · 17 Feb 2015

Hi again. Sorry, but just to add..... I assume that changing the head on the motorized valve would solve any issue with the microswitch?

I ask this because I've noticed that my Honeywell valves do have the dimple on the cover and looking inside confirms they have just the 2 mounting screws rather than 4 so it seems I'd be able to replace the head without draining down the system. I think replacing the head is within my capabilities wheras if it comes to draining down I might wimp out.

I assume the microswitch is part of the head arrangement? Worth me changing it?

misterdubya · 17 Feb 2015

luke-warmwater said:
Thanks again for your reply.

No, I'm afraid I dont have a multimeter, but I could get one and learn how to use it.

By using google?

For the price of a decent one, I'd of had your heating system fixed hours ago, with plenty of change (including the 200 odd mile drive up to Leeds).

I assume the valve body is ok?

luke-warmwater · 17 Feb 2015

I meant to add..... could I take the head off the HW valve and try in on the CH valve? They appear to be the same model number and this might determine if the microswitch is at fault before forking out £50 for a new head. It seems that neither require a draining down. Question is... what happens to the HW system while the valve head is off?

D_Hailsham · 17 Feb 2015

luke-warmwater said:
I assume that changing the head on the motorized valve would solve any issue with the microswitch?

Yes; but before rushing out and buying a new head we need to prove that is the problem.

Here's how to do it without using a meter.

The cables from the two valves should connect to a large junction box on the wall.

Turn the power off
Remove lid from box
Find the grey and orange wires from the CH valve. These connect to the microswitch.

Normally both greys will connect to the same terminal and the oranges to different terminals, but it can be the other way round.

Disconnect the wire which is on its own (make a note of which terminal) and connect to the pair. So you will have either two greys and an orange, or two oranges and a grey, in the same terminal. This effectively shorts out the switch.

Move the valve lever across to the Man position and lock it into the notch.
Set the room stat to a high temperature.

Turn power on and CH on at the programmer. (Leave HW Off)

The boiler should start and the rads heat up.

If the problem occurs, there is a fault in the boiler.
If it does NOT occur, the microswitch is faulty.

Make sure the lever is still in the notch then turn the power off.

Replace the valve head or get an engineer into check the boiler.

luke-warmwater · 17 Feb 2015

D_Hailsham - Many thanks for that brilliantly detailed and user-friendly explanation. I'll do exactly that tomorrow morning and let you know how I get on.

misterdubya - yes the valve body is ok.

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Boiler puzzle

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