Boiler delivers hot water but no heating - what's going on?

[saintgeorge]

Hi, it's all very strange!

I've got a Glowworm Fuelsaver Mk II model 50 connected to a Towerchron QE2 timer.

The pilot light went out yesterday in strong winds. I've relit it OK, but for some reason the boiler only bothers to fire up when the timer for hot water comes on. When the timer for the central heating comes on, the boiler does nothing. I've turned the room thermostat and the boiler thermostat up to full to check these are not the problem - they seem to 'click' OK.

I'm assuming that the problem is something to do with the pilot light having gone out, but it seems a bit odd that the boiler lights when one part of the timer says it should, but not when the other says it should.

Can anyone give me any ideas?

 

[Davycrocket]

Hi I don't know the boiler you name but If its a combi do not read on.

If it's not a combi and you have a storage tank in the airing cupboard and a 3 way valve, then your problem is probably a burnt out little motor inside the top of the three way valve. You can prove it by moving the lever on the valve to MAN OPEN. The Boiler will fire up. But if you have a combi ignore all this. If the motor is the problem it can be bought separately and replaced. Rgds

 

[saintgeorge]

Davy

Thanks for that. You're right, it's not a combi, and I do indeed have a little metal box in my airing cupboard. I'll give your suggestion a shot.

 

[Davycrocket]

Hi its me again
The three way valve is a very strange beast. !!

With the Timer water switch ON and the tank thermostat saying 'Tank not hot enough ' the boiler will fire up and the three way valve will be at a position for port A to be open. It is forced there by a spring. If the central heating it then turned on at the timeswitch and the room (or hall depending on where it is located) thermostat says 'not hot enough in here', the 3 way valve motor should run to a mid position, when both ports will be open and the boiler still fired up. If the tank then becomes hot enough , the tank thermostat switch will transfer and the little motor should drive the valve to the central heating only position.

Now here lies the problem !!! the motor stays energised with 240 volts applied to its coil even though the valve is hard up against the stop. and even stays there still cooking when the room stat says 'OK hot enough in here ' and the boiler switches off .
A motor will feel very hot in this condition and although it is the way it was designed to work, the motor will eventually burn out.
. For this reason , plumbers merchants sell lots of COMPLETE valves, and lots of REPLACEABLE VALVE HEADS. But you can also buy just the motor. It is easily fitted provided that the three way valve is in an accessible place. There are just 2 screws and two wires. and the motor comes with a couple of connectors. It is called a Synchron motor .

If your motor is NOT hot , it is probably burnt out. If you push the lever on the valve towards and PAST the manual position and as far as possible (to the right) the boiler and pump should fire up if the Timeswitch says heating ON and the room stat is calling for heat. Rgds
David C

 

[saintgeorge]

Ok, here are the results:

- thermostats all at full (incl tank)
- 3 way valve switch fixed in MAN OPEN position
- heating timer switch activated

...does nothing at all. Boiler doesn't fire up. BUT doing things in a different way:

- thermostats all at full (incl tank)
- heating timer switch activated
- 3 way valve switch pulled over to MAN OPEN position

...causes the boiler to fire up. But I have to hold the 3 way valve switch all the way over to the right in order to keep the boiler on - if I let it release, the spring pulls it back and the boiler goes off. Likewise, if I move the lever on the 3 way valve into the 'catch' that holds the lever in the MAN OPEN position, the boiler also cuts out. I have to hold it right against the edge of the slot holding the lever for the boiler to stay on.

Does this change the diagnosis? Have I got a dodgy 3-way valve, or is it something else? I am a bit bemused by the fact that the order in which I run the test makes a difference - ie the timer has to be on FIRST before I move the 3-way to the MAN OPEN position. Seems a bit odd. Grateful for advice - many thanks.

 

[MANDATE]

Whenever HW is included in the demand (ie HW only or HW/CH) the boiler receives its power through the cylinder stat. If HW is not in demand or is satisfied the cylinder stat turns off the power to boiler. But it is replaced with another source of power after the actuator quadrant has moved to the CH only position. This is through a microswitch in the valve head.
So first there needs to be power to the grey wire of the valve, secondly the motor in the valve head has to move the quadrant from mid position to CH only and thirdly the microswitch must not be faulty.
You've proved the microswitch is ok, just prove if the grey wire is live at the valve/terminal box. If it is live then the problem will be motor related.
Best to take the head off the valve spindle and watch the underside as you test it. The total movement should be in two halves. Ie slight delay at mid point. This is because of two separate power supplies, one to move valve over first half where it either stops or picks up the second power supply to move the valve over the second half. It all depends on what was selected and which side is satisfied or not.

 

[Davycrocket]

Hi
Sorry for late reply.

First about the auto/manual lever.
When it is latched in the MANUAL notch it is in the MID position and means both ports A and B are open. It is intended ONLY to assist in draining the system. However in this latched position with hot water timeswitch ON and cyl thermostat calling, then the boiler should be fired up and the pump running REGARDLESS of whether the little motor is burnt out or not . In your situation, with heating also tuned on and room(Hall) stat calling, then pushing the lever all the way to the right operates a switch which turns on the boiler and the pump. You could jam the lever in this position to warm the house up whilst you have a re-think. !!!

Things to check
1. With hot water ON at the time switch and Cyl thermostat calling (not hot enough) and with central heating OFF at timeswitch then the boiler should be fired up and pump running . In this situation the boiler and pump are fired up directly from the timeswitch and cyl stat contacts and the system uses no electrical parts or wires of the three way valve.
In this situation the system does not even know that you have a three way valve.
2. Whilst 1. above is happening moving the lever to the notch position should result in boiler and pump still running but rads now getting hot. even though you have not turned on ' central heating' at the timeswitch.
All you have done is manually put the valve into the mid position, although electrically, the system THINKS it is still just heating the water.
If you can NOT get 1. and 2. testing out ok , then there is a bad contact in the timer or a bad contact in the cyl stat.

If you can get 1. testing out OK there is no reason why 2. should not test out OK too.
Now
3. turning central heating ON at the timeswitch should produce no change at all, even if the motor was good
But
4. if you now switch hot water off at the timeswitch, or adjust the cyl stat to a lower temp so that it is 'satisfied. then the motor if its still ok SHOULD run to the heating only position and the boiler and pump should continue to run . You would normally get a boiler' off and relight' whilst contacts are transferring within the valve.

It seems to me that if 1. 2. and 3. check out as above but 4. does not happen, then you do have a burnt out motor. As previously mentioned it is a simple job to change it provided that the 3 way valve is in an accessible position. Buy the new one at a plumbing shop as it will be a lot cheaper than at places like B & Q.
Good Luck My tel No is 01925213446 and Email
cruikshankdavid at aol dot com

 

[Davycrocket]

Hi saintgeorge
I read through your test results again just now.
The reason that the results seemed different in the two sequences that you performed was because a switch inside the valve top metal box transfers when you push the lever all the way to the right but does not transfer when you leave the lever latched, as I mentioned in the last reply, in the mid position.
I now feel sure that your problem is the motor, as your previous tests have proved that the 'water only' condition can fire up the boiler and so can the ' heating ON' with room thermostat calling, with the lever pushed all the way to the right, which proves that a switch inside the valve head is also OK. So there is just one more unproven switch inside the valve head and the motor. The chance of the switch being the problem is about 1 in a 1000 whereas the chances of it being the motor are 1000 to 1. Change the motor !!! Rgds
David C

 

[ChrisR]

a switch inside the valve top metal box transfers when you push the lever all the way to the right

No it doesn't.

 

[Davycrocket]

To ChrisR

Chris I am surprised at your statement out of the blue

In a conventional Honeywell 3 way valve there are two switches one of them has its common connected to the WHITE wire which will have 240 volts on it when central heating is calling . This switch is transfered either by the motor driving the quadrant to central heating ONLY position . OR BY MANUALLY PUSHING THE LEVER AS FAR AS POSSIBLE TO THE RIGHT. When transfered this switch will send 240 volts out on the ORANGE wire to fire up the boiler, and is the ONLY way the boiler can fire up if Hot water is not calling.

With both heating and hot water calling, the same SWITCH when Not transfered at the mid position, and with the boiler fired up directly from the hot water also calling, feeds the 240 volts present on the WHITE wire via a diode to lock the motor at the mid point with pulsing Direct current.

And yes there is another switch which does another job, but the one I spoke of, the one you deny the purpose of is the one decribed above.

So what is your explanation? Rgds David C

 

[MANDATE]

Hi david! When I dismantled a potterton 3 port valve I noted the 2 microswitches were mounted side by side. I expected one cam to be positoned at mid position and the second at the CH position, but the second cam was only two or three degrees behind.
Perhaps this is what chrisr is thinking and the lever is not required to go all the way to the right. Well it is for the valve but not to trigger the microswitch.

 

[Davycrocket]

Hello mandate
Yes there are two switches , No 1 transfers just at mid position to remove the 240 v drive from the motor to allow it to stop at the mid position , held there by the 240v supplied on the white wire from heating required, then via the normally closed contact of switch 2, which IS still in its normal condition not transferred, and rectified to present the motor with pulsing DC which locks it at the mid point. Switch No 2 will only transfer when water heating is no longer required and either the water heating OFF switch in the timer, or the cyl thermostat satisfied supplies 240 v on the grey wire . This is passed on to the motor via the normally open, but currently closed contact of switch 1. The motor starts to run, and switch 2 transfers after a few degrees of movement of the geared quadrant and passes 240v to the boiler and pump via the orange wire. The boiler and pump will have momentarily switched off when hot water was no longer called for. The motor continues running via the 240v IN on the grey wire from water not calling until it stalls in the central heating only position with the full 240 V STILL applied. This is why these motors eventually burn out . Rgds David C

 

[saintgeorge]

Wow, loads of replies! Thats great - thanks folks.

I'll print this all out and check that the descriptions given match my circumstances. David seems to have been a regular visitor to my flat given the accuracy of his predictions so far, (yes, it's a Honeywell box...), so I'll check this all out and see how I can get myself a new motor. Let's face it, it's got to be cheaper than calling out an engineer to prod my boiler to no avail...

Watch this space...

 

[Davycrocket]

Hi there saintgeorge

Do you do Ebay ? There are two motors at item No 290058128182 Ending soon !!

Rgds
David C

 

[MANDATE]

David! The point I was making was regarding the comment by Chrisr. The lever only needs to go a couple of degrees past the mid point to trigger the second microswitch, not all the way to the right as one may think.
To go a little deeper, if the second microswitch fails you can end up with the valve in the CH position but no power coming from the orange wire, so no boiler flashup and motor not the problem.
Should the first microswitch fail, or the power on the grey is absent then actuator will not be able to get beyond mid point, so it will never trigger the second microswitch and again motor not the problem.
I agree motors seem to be the biggest problem, but you need to make sure your not replacing it if it ain't broke.