CH problem - syncron motor duff + ghost signals

[Ellwood]

I wonder if anyone can help...

I have a fully pumped HW and CH system with following controls:

- Wickes (Landis & Gyr) LWB200 programmer set to '16'

- Wickes (Landis & Gyr) MAV-322 3-port mid-position valve

- Wickes (Landis & Gyr) cylinder stat

- No room thermostat; TRVs fitted to all rads except bathroom + one other

The system has been running sweetly since I re-plumbed / re-wired / fitted new circulator and controls to the airing cupboard area about five years ago.

A few days ago the system stopped sending hot water to the radiators when controls were calling for either CH only or HW+CH. Quick tests of all modes showed the HW side of things working fine - either with HW only or HW+CH being called). With only CH demanded, pump and boiler do not fire up. Manual override lever on mid-position valve works fine, allowing water to rads for a short time - as long as long as pump and boiler is running (ie system calling for HW or HW+CH). With only CH demanded, a careful (insulated!) manual push of SW2 inside the valve head kicks power down the orange lead and fires up pump and boiler. The upshot of all this is that I can say with reasonable confidence that the synchron motor inside the valve head needs replacing but the valve itself and the switches are probably OK. I have also confirmed tha the cylinder stat is OK. So, I have bought a replacement synchron motor from Wickes and am raring to go with the replacement, but...

... I'm a little puzzled with the results of the checks of the programmer's signal outputs, done just with a simple 'live-checker' screwdriver:

The 'CH On' signal is fine - and runs to the white wire of the valve. The 'HW On' signal is fine when controls are calling for HW - and this runs to T1 (input) of the cylinder stat. But, the 'HW On' signal wire shows a half-strength indication on my screwdriver light when controls are NOT calling for HW - even when I check it disconnected from the cylinder stat. (Huh?) The 'HW Off' signal is fine when controls are NOT calling for HW - and this runs to T3 (the closed-when-hot output) of the cylinder stat, plus the grey wire of the valve. But, the 'HW Off' signal wire shows a half-strength indication on my screwdriver light when controls ARE calling for HW. (Huh again?)

I wondered if I had a double fault so I checked all logic and connections in the circuit at least three times - with all but the essential wires disconnected - and I came to the conclusion that the programmer was sending these ghost signals, so might be dodgy. So, I've replaced it with a fancier model (RWB9, which has 5/2 capability, which I was prepared to pay an upgrade premium for anyway). Hhmmm... new programmer now installed and set up... and the circuit behaves exactly as it did with the old one... I still have these mysterious half-strength signals where I expect none.

I wonder if any of you nice people could advise me: is this normal? Can I expect to have these 'ghost' signals, which perhaps don't interfere with the operation of the circuit? At the moment I don't feel inclined to change the synchron motor until I'm sure I haven't got an underlying problem elsewhere, which might damage the new motor if I go ahead and fit it.

Any help much appreciated.

Sorry for the long post ;-)

[end user]

its probably the type of batteries you use in your tv remote control

[Set Square]

Is your "live-checker" screwdriver the type with a little neon lamp inside which glows when you put the tip on a live wire and put your thumb on the other end?

If so, throw it away and get a *proper* means of checking for live-ness. Your screwdriver will glow dimly due to inductive pickup - when you touch a non-live wire which runs parallel to a live one. What you need is a decent high impedance multimeter, set to measure AC volts. Measure the voltage between each programmer output and neutral, and you'll find out which ones are *really* live.

[Ellwood]

Gulp - 'fraid so.

Thanks for the good advice, Set Square. I had wondered about the possibility of the programmer 'leaking' potential into the 'off' wire, but I hadn't given a thought to inductive pick-up from parallel wires.

Cheers.

[John Stumbles]

Actually a high impedance voltmeter may also give misleading results: what you want is a not-so-high impedance one. The sort with a real needle (rather than LCD) will do. Alternatively the sort of voltage tester comprising a pod with 2 LEDs in it and a probe on one end, with a wire coming out of the other to another test prod.

[Ellwood]

OK - I suppose I walked into that, talking about ghost signals.

P

[James Salisbury]

Actully the OP may have been spot on, I seem to recall the orange wire is back fed from the valve to about half mains....

[Ellwood]

'fraid not James - these 'ghost signals' appear even when all the wires to the valve and stat are disconnected. I think Set Square's parallel inductive pick-up (between the HW On and HW Off wires, which run very much in parallel in my system) explanation is the the most likely one at the moment. I think the fact that they work 'vice versa' gives it away: when HW On is live, HW Off shows a ghost signal; when HW Off is live, HW On shows the ghost signal.

Cheers anyway.

[Ellwood]

Job done. :-)

I took Set Square's advice and checked for 'live-ness' with a proper multimeter and all 'signals' worked out OK - either 240v or 0v. So the neon screwdriver must have been picking up some wigglies by induction - as Set Square said. Phew - paranoia over.

The replacement synchron motor on the mid-position valve was fairly easy to change and very reasonably priced (£15 in Wickes). My only gripe was that it came with bare wire ends plus a pair of insulated crimp-on splices, rather than proper spade connectors.

Many thanks to those who responded to my first post to uk.d-i-y. What a helpful bunch you are :-)