Hot Water won't run if Heating is on

[Nerdio]

Just as a background, I have for a number of years run my Heating continuously with Hot Water chipping in 3 times a day, and this has all worked fine. (Heating is controlled by a programmable stat.)

I now have an odd situation in that the Hot Water will not run if the Heating is on, which is a problem I had years ago when I did not have a HW Off signal.

I have changed the Head on the motorised 3-port valve, but still it will only run one or the other. (Never sits ion the middle).
The cylinder thermostat has been removed, and the wiring re-done. The stat seems to operate smoothly enough, and is not that old. Hot Water, once it has run is fine.

I have also checked the wiring in the programmer, and that all seems to be intact, except I don't seem to have a CH Off wire. The system has worked in the past, so not worried about that.

I think now, that the programmer maybe knackered. It is quite old. The programmer was also not located correctly on the back-plate meaning it could swing on the contacts and top hinge. The contacts look OK, and I have cleaned the pins with a contact cleaning 'rubber'. Still no joy.

Any ideas?

3-port valve is a Drayton MA1
Programmer is a Honeywell ST6400C
Cylinder Stat is a Danfoss AT

Thanks in anticipation

 

[1983]

check to see what voltage is on the orange wire when hot water on.
if its not 240vac then work it back through the cylinder stat to the programmer to see where the fault is.
You can also check to see what voltage is going to the syncron motor when heating and hotwater on.
heating is power to the white wire.
there is no heating off wire with this valve.
Hot water off or satisfied power to the grey wire.

 

[Nerdio]

Thanks for the reply, and tip on where to start.

My programmer has been moved upstairs from downstairs, and some of the wiring seems to still be used (ie std. T&E cable disappearing out of wiring box, and programmer has 3 core flex coming in). I have enough electrical savvy I think to work it through.

I've had a look for some wiring diagrams on the web, and there seem to be 4 types of system W, S, Y, and C. I guess these are for different configurations. Are there any clues to identify correctly which system I have/ should have?

Thanks again for the reply. I won't be able to do anything about it for a few days though.

 

[CBF]

you have a y plan with a mid pos valve, s plan is two seperate zone valves

 

[Nerdio]

It's been a few days since the last post, and I have been away, so have only just got a chance to look at this.

With the heating set to Constant, and Hot Water off I don't have any volts on either the Orange or Grey Wire for the mid-point valve (which was on 'H'). If I press Extra Hour for the Hot Water, the light comes on, but still no volts. But if I then turn the heating off, volts appear on the Orange Wire (HW ON). Turning the Hot Water off then puts volts on the Grey Wire (HW OFF). The Valve moves to 'W'. If I put the heating back on, the volts for the Hot Water happily come on and off as I switch it on and off.

I then turned the Water off, and the heating off and back-on. Now the heating has come on. The White, Orange and Grey wires are all live now. This seems wrong! The HW is off!

Is my original thought about the programmer being knackered right?

Any help, comments, or thoughts are appreciated.