CH 3-port valves - what a nightmare

[Michael Kilpatrick]

Despite being a clever design, they couldn't be more obtuse, could they?

I'm trying to work out why, this morning, the central heating came on despite the timer control being set to off and the thermostat turned down. Hot water was fine, I think, and the thermostat on the cylinder is certainly activating the boiler when appropriate. Controller is standard old thing with a timer and "off-cont-twice-on" settings for HW and CH.

I assume it must be the 3-port valve (Honeywell Sundial Y plan), but once all the pipes everywhere are hot it seems actually rather hard to test it without waiting for everything to cool down again in order to see where heat is being delivered when I mess about with the controls.

If I think the motor has gone, then if I disconnect all the wires should it stay in "how water only" mode?

Also, I can't find out what the manual override lever on the valve is for!!! Is it supposed to set it to "heating only", "hot water only", or "both on"??

Michael

[Roger Mills]

It sounds as if the valve has stuck in the mid position. When that happens, the boiler will fire (and the pump will run) whenever there is a demand from the HW stat - but water will flow round *both* the HW and CH circuits.

It depends on exactly what's happened. If the 'wet' part of the valve has seized, nothing you do to the actuator (the electrical part) will make any difference. If the actuator has simply got confused (and it *can* happen!), powering it down completely - at the FCU which feeds the whole system, not just at the programmer - may 're-boot' it and make it work properly again. [If you need some help to determine which it is, come back.]

It moves the valve - against the return spring - to the mid (both on) position, but not all the way to the CH-only position. It makes it easier to fill the system with water by opening both circuits at the same time. If it's working properly you'll feel quite a lot of resistance from the spring and gears as you open the valve, and if you then let go of the lever, you will hear the gears whirring as the spring closes the valve.

[Michael Kilpatrick]

Thanks. In the end I'd guessed that it must be the mid-position as I eventually discovered from info on-line that the spring defaults to "HW only".

With regard to my faulty valve, I would have thought it would not be possible to move the override lever if the valve were physically jammed, but it moved (with resistance, as expected) and also returned with the spring. Suppose it depends if the physical connection between valve and actuator can break or slip if the valve jams?

I've cycled the circuit breaker in the fuseboard and I'll see what happens...

Michael

[Roger Mills]

Did you test its movement with the lever *before* you'd cycled the power, or not until afterwards?

If the latter, it could have been electrically 'stuck' in the mid position, and cycling it may have cured it.

If the former, I suppose it's possible that there could be some crud lurking inside the valve which is stopping the flap from closing off the CH port completely - so that you still get some CH flow when only HW is selected.

Although unlikely, there's an outside chance that there's an electrical fault which is telling the valve to go to the mid position when it shouldn't. When this problem occurs, can you still feel resistance if you move the lever, or does it flop about freely?