HW only heats when CH is also active... but actuator is good

[Ytee2]

Hi All,

I have a really weird (to me) issue/feature in a house we've just moved into.

The CH and the HW work perfectly fine when they are both active. That is, when both are switched on at the control unit. However, if I switch the CH off but leave the HW on, the water doesn't heat. The boiler doesn't fire up, nothing happens at all in fact.

At first I thought this must be the actuator valve, so I had that changed by a plumber, but it hasn't made any difference. I can see that the actuator is working though. If I enable the CH and disable the HW, the valve flips over to 'H' just like it should, and flips back to 'W' when I do the opposite.

I've had the boiler serviced as well and there's apparently nothing wrong with that.

My system comprises a high pressure HW tank (a Gledhill, installed by the previous owners), and in addition to the actuator there is a second 2-port valve running between the 'Primary Flow' of the tank and the heating pipes. I'm not sure what that's doing, or whether it could be related. It seems not, since the heating does work fine when both CH and HW are switched on.

I'm a bit lost. Could this be a wiring fault? Or, is it just a feature of the high pressure tank having been installed into a system that didn't have one originally perhaps?

Thanks in advance...

 

[SJB060685]

This requires someone with experience and a multimeter. I suspect the end switch in two port valve isn't making.

 

[steadyon]

1. The two port valve in the primary flow to the heating coil is there as part of the safety system for an unvented cylinder. It will be controlled by a thermostat built into the cylinder, and will close when the water has reached its pre-selected temperature, regardless of what the rest of the system is doing.
2. As SJB suggests, some investigation with a multimeter is required.
3. As the 2 port valve is part of the safety system, any work on it or the rest of the cylinder requires an engineer with a G3 qualifiaction.

 

[Ytee2]

Thank you both for the replies.

I'm curious though, why would that valve being faulty affect whether or not the water heats up without the CH on?

One situation I've tested is when the water in the cylinder is cold. I switch the HW on, but leave the CH off, and nothing happens. In this case, it's not because the correct temperature in the tank has been reached already surely? The water is still cold. If I then switch on the CH, everything fires into life, and the water heats up normally, gets to temp, and stops heating... just like it should.

 

[SJB060685]

Attached is an image for how your particular system is/should be wired.
Everything you said above suggests to me the end switch isn't contacting despite the valves being open, which is what I initially said. As it stands you are getting no switch live to boiler and pump despite the valves open. Multimeter probes in the right place will rule this in or out, although as said above by steadyon you need a G3 registered engineer to find and rectify the problem.
To be honest the person who replaced your three port valve should have stuck around long enough to find out if they had fixed it, if I was called out to this and replaced the valve and charged you for it, then I would be expected but also inclined to return free of charge.

 

[Ytee2]

Attached is an image for how your particular system is/should be wired.
Everything you said above suggests to me the end switch isn't contacting despite the valves being open, which is what I initially said. As it stands you are getting no switch live to boiler and pump despite the valves open. Multimeter probes in the right place will rule this in or out, although as said above by steadyon you need a G3 registered engineer to find and rectify the problem.
To be honest the person who replaced your three port valve should have stuck around long enough to find out if they had fixed it, if I was called out to this and replaced the valve and charged you for it, then I would be expected but also inclined to return free of charge.

Thanks, that diagram is really helpful. Don't worry, I'm not planning on touching any of this myself

To be fair to my previous plumber, I called him out specifically to change the actuator (which was definitely stuck before) rather than 'fix the whole issue'. Now that's done, I can see the actuator is now doing what it should be doing, but this particular issue remains.

Certainly useful to know that this is a genuine fault as opposed to just a bizarre feature of the system, so I'll call someone back in to take another look.

 

[Ytee2]

Problem solved. It was the two port valve as you both thought. Thanks for the tips.

 

[Aquarius]

To be fair to my previous plumber, I called him out specifically to change the actuator (which was definitely stuck before) rather than 'fix the whole issue'. Now that's done, I can see the actuator is now doing what it should be doing, but this particular issue remains.

To be fair he should have got the whole picture and not gone off the customer’s request. If the actuator was stuck, and a new one fitted, I’d have expected the problem to disappear, as all the gubbins are in the new head (actuator). As @SJB060685 states, it should have been tested to make sure that it works correctly and he hasn’t fitted a dodgy one (a lot of Honeywell failures recently), if it was just a motor replacement, should still be checking the correct operation. Let’s see what the other engineer fathoms out.