hot water/heating problem (again)

[skuba]

in my house we have hot water and heating both on constant, but about a week ago they both suddenly stopped working. the pilot light was still lit in the boiler, so i power-cycled the programmer, mid position valve, and pump in the airing cupboard. i' managed to get the heating or hot water working by faffin with the lever on the valve, but i can't get them both working at the same time. i think there may be a problem with either my programmer or the valve...
- when hot water is ON and heating is OFF, the pump kicks in and the boiler ignites
- when heating is ON and hot water is OFF, the pump does not kick in and the boiler does not ignite
- when both hot water and heating are ON, the pump kicks in and the boiler ignites

is there a way to manually force the valve to be open for heating and hot water? a similar thing at exactly the same time last year! could this be related to the temperature dropping outside?

thanks

 

[75pete]

What did you have to do last year to fix the problem? Your type and make of boiler?

 

[stem]

If you have a three port valve, the boiler is primarily controlled by the hot water cylinder thermostat. What I mean by that is: of the three possible positions of the valve, in two of them, the boiler is controlled by the cylinder thermostat (Hot water only / Hot water and central heating) It is only the third position of 'central heating only', that the boiler is switched by a microswitch inside the motorised valve.

From your list of symptoms above, it would appear that it is indeed only when the central heating is selected to be 'on' on its own, that the boiler does not operate. It is possible that this microswitch is your problem. It's easy to check if you have a multimeter and can use it safely. Isolate the orange wire that comes from the motorised valve, and with the heating only set to 'on' check to see if there is mains voltage present on the orange wire. There should be, because this is what operates the boiler when heating only is on.

It would appear that the room thermostat is functioning, because the valve is moving from the default 'hot water only' position if the radiators do warm up when the both heating and hot water are 'on'. Only the signal to run the boiler which is provided by the microswitch appears to be missing.

 

[skuba]

that sounds correct stem, the only thing i would add is that when hot water and heating are both on, i can only have one or the other working, not both. the way i choose between the two is by fiddling with the lever on the side of the motorized valve. there's no logic to it, but through trial and error i can get hot water on OR heating on, but not both at the same time

do you think it would be worth having a local plumber to simply replace the motorized valve? how much is this likely to cost approximately?

thanks

 

[stem]

OK then. If you are manually moving the valve, then it maybe that the valve motor is not operating. I'm sorry don't know how much it would cost as I've always changed my own. But it would be better to get someone in who can carry out the necessary tests and determine where the fault actually is rather than swap parts in an ad hoc fashion. The fault may be with the room thermostat. or wiring. Less likely, but it can happen, especially if you have a battery powered thermostat. On most valves, you can replace the valve actuator, so don't have to drain the system down, a handy DIYer should be able to manage it in 20 minutes or so.

 

[Agile]

I would charge £84 to diagnose the fault and £24 to fit a replacement motor valve motor providing that its one of those which is reasonably easy to change.

The metal bodied ones are normally quite straight forward but the plastic bodied ones can be a right pain and often plastic bits inside are either already broken or break when you open it.

Tony

 

[skuba]

i've just nipped home at lunch to take a photo of the motorized valve and the heating AND hot water both appear to be on! i've got no idea what's happening, there doesn't seem to be any logic to it! i've attached a few pics of the motor valve. as you can see it's got a lever on the front and something sticking out of the side. from what i can tell, the thing on the side does nothing. i've pushed it in a little but it doesn't seem to do anything. i can't pull it out any further. however, the lever on the front moves when the power is on, but once it's in position you cannot move it manually. if i turn off the power, the lever moves back over to the far left on it's own (presumably closing the valves) and then i can then move it back over to the right freely, but it always 'bounces' back to the left and i never know whether i've opened up hot water or heating, or both, etc. however, with a bit of trial and error switching it off/on and moving the lever i can influence whether it's the hot water or central heating that starts to work...

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[stem]

At rest, the valve sits at the hot water only position (the central heating port is closed off) where it is held by a spring. In this position when you slide the lever you will feel the resistance of the mechanism and when you release the lever, it will be pulled back to rest by the spring.

When heating and hot water are required the motor winds the valve to the central position so that both hot water and heating ports are open.

When heating only is required, the motor winds the valve fully across so that the hot water port is closed off.

Once the motor has moved the valve from the rest position, if the lever is moved, there will be less or no resistance, and it can feel loose and disconnected. The main purpose of the lever is so that both ports can be locked open when the system is being filled with water.

Whilst all 3 port valves are similar, yours looks like a Drayton that has been re-badged by British Gas. You can find a manual here.

One of the foibles of a 3 port valve is that it can stay energised, even when the programmer has turned off, and this can cause some confusion.

 

[skuba]

unfortunately, i think i may have spoken too soon. it seems like the radiators are cooling down whilst the water is still red hot, so i'm guessing that at some point this morning the heating valve has closed off

thanks for the link to the manual, i've taken a look and i've also googled drayton 3 port valves. i've found an installation guide which says "When the manual lever is moved to the right and pushed in to ‘lock’, both outlet ports A and B are open, it automatically releases when the valve is powered."

the problem is, the valve is powered from the same supply as the pump and the programmer, so i can't leave the valve turned off. the statement above seems to suggest that when the valve is powered the lever is going to automatically revert to it's resting position?

 

[stem]

I suspect that the valve has been moved by its motor to the heating and hot water position. At this point the boiler will be under the control of the hot water cylinder thermostat and is running, so both hot water and radiators heat up. Then, after a while, when the hot water was up to temperature, the cylinder thermostat would turn off the boiler, and the valve would wind to heating only. Normally when this happens, the microswitch in the motorised valve would take over and keep the boiler running. If the microswitch was faulty it wouldn't, and so the boiler and pump would go off. That means that the valve could well be in its correct position, but as the boiler and pump are off, everything cools down.

However, the only way to be sure is to check the wiring with test equipment and find out if the right control signals are there or not. Alternatively, you could try swapping the valve actuator and see if that fixes it. If not, it's back to the drawing board and you will have a spare for when it does fail.

 

[skuba]

that sounds exactly like what's happening stem. as we leave our heating and hot water on constant anyway, i think the best option would be to see if i can manually 'lock' the lever in open position for both water and heating, thereby bypassing the need for the microswitch

do you think this is possible on the drayton? thanks again

 

[stem]

Fixing the valve manually open will probably not work, because :

1. Manually open is usually the central position, (remember it's really there to allow the system to be filled with water) so probably not far enough across to operate the microswitch, which would be needed to start the boiler up when heating only is required when the hot water is up to temperature.

2. If the microswitch is faulty it doesn't matter if it was operated in the manual position it still won't start the boiler anyway.