CH radiators always on

[Bill]

For once this is my problem rather than sons or daughter.

Our central heating appears to be a basic S-type system with a Vaillent Ecotec Plus 428 boiler, Siemens RWB2E timeswitch and RCR10 wireless room stat. 2 Zone valves, one for CH, one or hot water. All installed by a local company about 10 years ago.

Because of my persistent bad back, I don't feel safe climbing into the airing cupboard and measuring voltages after taking covers off the boxes there. I have reset and checked the 2 controllers and all lights come on as expected as dials are turned.

For about 5 days now the heating has been staying on all night. I've been looking at the diywiki site and can't see how, with the stat and timeswitch set to OFF, the system can be running. I can't believe that both timeswitch and stat could have both failed at the same time.

Is there something I'm missing?

[Michael Chare]

Stuck Zone valve?

[RobertL]

On my CH zone valves you can feel with a finger underneath and find the spring-loaded lever that should be moving the valve. You can feel this change from being 'loose, to 'tight' when the valve opens/closes without needing to take the cover off.

The firing of the boiler is usually determined by the actual position of the physical valves, rather than what their commanded position is. So if they get stuck open then the boiler fires.

[Bob Minchin]

Is there a frost protection stat that is telling lies? This would normally be wired to bypass both timer and room stat.

[Bob Minchin]

Also check if the "demand" terminal on the boiler is live. If it is not live and yet the boiler runs, then suspect the control board. If the demand terminal is live then it is the external controls giving wrong instructions to the boiler.

[GB]

I find that the maximum dosage of Ibuprofen (400 mg) does not work for me at all, even taken over a prolonged period. But a couple of doses of

600 mg does. Be aware of the serious risks from overdosing, though. And, this is not a recommendation, just a comment on my personal experience.

[tabbypurr]

the only sure way is to measure voltages to locate the problem. You might be able to pin it down by seeing the result of operating the various controls, maybe.

NT

[Roger Mills]

Yes! On an S-Plan system, the timers and stats drive the zone valves - and it is the zone valves which actually switch the boiler and pump on. So, if the CH zone valve sticks in the open position - or if the contacts in its micro-switch fuse together, the boiler and pump will run continuously regardless of what the timers and stats are doing.

[John Rumm]

Possibly...

Have a look at:

Note that the grey wires to both zone valves is permanently connected to live. Hence if for any reason the valve caused to be in the "open" (i.e. heating on) position, then its internal microswitch will output a call for heat on the orange wire to the boiler / pump etc.

So you have two possibilities; One, both the programmer and the stat are erroneously calling for heat all the time (seems unlikely), or two; the CH valve is physically stuck open (or at least its microswitch is stuck in the activated position), and hence if feeding a spurious call for heat to the boiler even when the programmer / stat are not requesting it.

The fact that the rads are getting hot would suggest that the valve is physically open - rather than it just being a switch or wiring fault.

My guess would be the valve body (i.e. the wet bit) has become stiff, and hence the spring in the motor head is not strong enough to pull it to the closed position when the valve is in the off state. The normal solution would be to take the valve motor head off, lubricate the shaft of the valve and twist it back and fourth while gripping it with a pair of pliers. You may find that with the valve not energised (i.e. programmer CH off), a few sharp taps on the side may free it.

[Davey]

That is exactly the fault that my system had. Even with the Programmer set to 'Off' for both CH and DHW, the boiler was still getting a 'Run' instruction. Removing the zone valve actuator and working the valve stem fixed it.

[Bill]

Thanks, John, and the others who answered. I've been pretty slow because SWMBO doesn't believe there is a problem.

I'm now pretty certain that it is a stuck zone valve, but with the combination of its position and my back, I'm going to have to "get a man in" to sort or replace it.

Taking a hammer to it failed, but was fun.

[Bill]

Interesting. Trouble is, I daren't take more than the recommended dose because of all the other tablets I'm taking.

Hard to tell if the standard dose does anything, but I _think_ there is a bit of improvement in the back, so I keep up the tablets and exercises routine.

[GB]

This was recommended to me by a back specialist. At the time, I had really terrible back ache. So bad that I fainted from the pain on one occasion.

[John Rumm]

If you can reach it well enough to feel the manual lever that is on the side of the valve, when its de-energised it should be held against one end of its travel by the spring - as you move it by hand you should feel resistance, and hear the gearbox / motor whirr as it moves. When you let go, it springs back to the start.

If however its "floppy" and you can leave it at any position in its travel, with no resistance to movement, then it is definitely stuck.

[Bill]

In message , John Rumm writes

Yes, been there, done that and it's floppy. That's when I decided we would have to get a man in.

Many thanks for the very thorough descriptions. With the postings here and some Youtube videos, I now feel like a theoretical expert on zone valves.