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Hi folks, I’m looking for a little expert help with the central heating/hot water in my house. I tend to fix most things myself but this one has me flummoxed.
My central heating is a three zone system, two heating and one hot water. The heating zones are working OK but hot water not circulating. My first thought was the motorised valve so I manually opened it, turned on the hot water on its own. I was expecting this to circulate the hot water but the circulating pump and boiler did not come on. Turning on a heating circuit and the hot water circulates through the tank ok. I then thought it must be the stat on the tank faulty and not signaling a demand for hot water. Changed this and still no change.
A plumber mate thought it was likely to be the motorised valve but I am not sure as manually opening the valve still doesn’t resolve it. It’s expensive to change the valve then find out it’s not that. I also wondered if it might be the time clock, my next step is to try bypassing the time clock to see if that is the fault.
The valve has a micro-switch inside it which energises the pump once it's open.
DHW TIMER -> VALVE OPENS -> PUMP AND BOILER RUN SIMULTANEOUSLY
Either the switch has failed (though they usually fail closed making a mockery of the tank safety stat requirements) or the motor has failed and isn't opening the valve at all. Or the tank thermostat could have failed open.
I'm guessing you have an "S-plan" setup but with an additional room stat and motor.
Test steps:
1. Check for 240V at timer switch when HW is on.
YES: Go to 2
NO: Replace timer.
2. Check for 240V on motorised valve (brown wire usually, grey is permanent live)
YES: Go to 3
NO: Problem lies in the cylinder stat.
3. Check for 240V on boiler switched live (ensure heating demand OFF first).
YES: Should all be working
NO: Problem lies with motorised valve.
You could troubleshoot the wiring centre with a meter (it's not complicated) but to be honest I would just buy another valve and swap the head over.
Wot he said.
changing the valve head rather than the whole valve is relativly easy and not expensive. No need to disturb the water at all
changing the valve head rather than the whole valve is relativly easy and not expensive
Even cheaper to change the motor. I'm not saying it's necessarily your motor but I've had 2 three-position valves fail (over 20+ years so I'm not complaining) and both times it was the motor. A quick look on Screwfix has a motor at £20 and a valve head at £80ish so it might be worth a punt. 2 wee screws and a couple of spade connectors so even easier than wiring in the head.
Even better. ^^
Though would recommend whipping the top of the valve off first to check the motor isn't soldered in. Also doesn't solve the problem if it's the microswitch at fault.
Screwfix can be stupidly expensive for stuff like this, often cheaper to shop around and buy online (ie Danfoss stuff from other merchants is less than half the price it is on Screwfix).
But if you've manually opened your motorised valve and it hasn't resolved the issue then surely it isn't the motorised valve...unless the actual valve the motrorised bit is trying to open. Have you tried removing the motorised head and manually opening the valve to check its free and operational?
If you have a multi meter it is easy to establish if the system is receiving all the right electrical signals so assuming that side is OK then you're into the various actuators in the system.
As above, if you are opening up the valve manually, and it isnt firing, then it is likely to be the microswitch inside the valve.
To see if it is the valve head microswitch,Turn off, go to the wiring centre, find the 5 core cable going to the HW valve. Open up the valve manually, connect up the grey and orange wires, with a fly lead, in the wiring centre,
The boiler should then start up and fire the HW when you turn it on.
Just feel the pipes leading to the HW tank to feel if they get hot.
If so, it will be the microswitch.
I think its a false economy changing just the switch, change the full head, as something else will be wearing out if one part has already failed.
As Flaperon said, Screwfix are very expensive for common bits. If your immersion is working order from e-bay and wait. I've just had the programmer unit fail while tidying the wiring up on my system. Screwfix £96, e-bay £42 delivered for new in box unit.
Manually opening a Honeywell valve will not cause the boiler to fire as it doesn't move the cam far enough to make the microswitch. Other valves are similar but I'm not up to speed on all of them.
If you have a Honeywell valve, pull the lever over quickly and quite hard and you can just about make it make the switch but only for a second. Test with a multimeter, if wired correctly, grey permanent live, brown live when programmer or clock calls for demand, then orange if thermostat isn't satisfied (in other words cylinder is colder than set point). If you've got 240 on brown but not orange then most likely motor. Simple to change, 2 wires, no messing in junction box (which are usually a mess)
Just getting back to reading your responses now folks, work was crazy today. It’s an s plan system with an additional valve yeah, Honeywell valve and it could be The motor, I changed it before.
I was thinking it wasn’t the motor as the hot water demand wasn’t there with the tank stat fully up, hot water circuit on and valve manually opened. From what you are all saying it’s likely to be the micro switch and I’ll test that tomorrow. At least it’s a simple fix though not cheap for the valve head.
You never cease to amaze me in this forum, it’s like an encyclopaedia
I replaced a motorised valve recently but I am actually convinced it was just the connection that was loose.
Manually opening a Honeywell valve will not cause the boiler to fire as it doesn’t move the cam far enough to make the microswitch.
I didnt know that, and I've done the Honeywell Installer course!
Next time you have a valve in your hand, whip the cover off and push the lever across and you’ll see what I mean. Then do the push it quickly method and you’ll see it make briefly, really simple way usually of diagnosing motor as if you’ve got demand from everything else you should hear pump / boiler start for a second. Obviously not fool proof but I change more synchron motors than anything else on a heating system.
Standard of teaching has gone down on the course then, mind you was about 20 years ago I did mine I think!