Hot water problem!

[landbeach]

I'm a bit stumped!
Girlfriend had a new boiler and controls installed circa 2 years ago. gas cindensing boiler, 7 day timer/controller with independent heating and hot water controls, and a wireless room thermostat.
Recently hot water has only been working intermittently and there's been no reliable/consistent way of getting it going again once it's stopped. Lots of fiddling with the motorised valve, powering everything off them on again works sometimes. (Immersion heater hasn't been used since she's been there - and isn't working).

There's only one motorised valve in the system - a BGMVSP -2 with 5 wires, inlet from pump and 2 outlets to hot water and heating. When I manually operate this and hold it in the open position the pump starts running and the boiler will fire and we get heat through both h/w and c/h. As soon as I release the lever the boiler shuts off. No combination of actions gets the valve motor to operate. Using the timer/controller doesn't fire up central heating or hot water, independently or together.
I presumed the valve motor was defective and have replaced the valve head with a Drayton ZA5, wiring like for like. (The valve itself moves freely). All 5 wires are connected. Yet the problem still exists exactly as before, so the valve probably wasn't the issue after all!

Looking at online wiring diagrams I can't quite work out what system I have. Can't be S-plan, or Y-plan, and I presume the 2 position valve head on a three port valve is acting as a diverter, and the system is something like a W-plan with hot water priority? The micro switch in the valve is definitely in use. So what's wrong with my system?

I'm wondering if the problem is actually the cylinder stat - and that it's not sending power to the valve? Any ideas welcome! Have I missed something?

Thanks in advance for any help!

 

[muggles]

Oh wow, so many words and yet so little information!

Pictures would help, as would make/model of programmer. I'm also unclear as to whether you have 2-port or 3-port valves. What warranty did British Gas give on their work (assuming from the BG valve that that was also new? )

 

[landbeach]

Thanks niggles - Sorry for the long explanation - was trying to give background in the absence of specific knowledge!
The 'new' installation was done by a local contractor circa 2 years ago and g/f has no idea who it was as was done under a 'scheme'. She has no paperwork!
The BG valve looked older.
The valve head only has two positions, but the valve itself has one inlet from the pump and two outlets - one to hot water tank, the other to the rads.
Will post photos later! Thanks!

 

[landbeach]

Sorry muggles. Predictive text changed you to 'niggles'

 

[Agile]

Sorry muggles. Predictive text changed you to 'niggles'

Perhaps more appropriate?

 

[Hugh Jaleak]

Possibly a Y plan that's wired wrongly.... Does this http://octaveblue.co.uk/central_heating.html help?

 

[ianmcd]

you have a 3 port valve or Y plan and by the head that you swapped is not compatible, the ZA5 head is for a 2 port zone valve and cant be used with a three port valve

 

[landbeach]

Ianmcd - thanks, I did wonder that when I was looking at the wiring and programmer - but it seems a little odd, as the old BG head was a 2 port model, and g/f said she hasn't ever had a problem before.
Is there any way I can tell from the valve itself whether it's a 3 port, or just a diverter?

 

[landbeach]

Possibly a Y plan that's wired wrongly.... Does this http://octaveblue.co.uk/central_heating.html help?

Thanks Hugh. definitely helpful thanks - especially if I have to replace with a different head and check I have y-plan setup.

 

[landbeach]

Right - seem to have got h/w working. Found a loose connection in terminal box on the blue wire from the programmer.
Turned power back on, selected h/w and pump and boiler fire. Cylinder stat working ok.
But, c/h still seems to be a problem. With h/w off and room stat set high nothing happens at all.
Even if I slide the motorised valve across manually the pump runs, but boiler doesn't fire. And then the hot water doesn't work unless I power off system and restart it.

 

[landbeach]

Update. Have replaced the ZA5 actuator with an MA1, and have checked all wiring is as per Drayton instructions. All looks fine.

When Powering up system I can get hot water working about 50% of the time. When hot water is working ok, turning cylinder stat down shuts off heat and after a few mins pump stops - so seems ok. Turning thermostat back up and it fires ok! So all good. But, when I switch off hot water at programmer and then switch back on, nothing further happens!

And as for heating - still nothing. No valve movement, no pump, no heat.

Haven't really used a multimeter before so have shied away from using one so far. Seems like now is the time to learn!

 

[nortonj]

Check wiring centre for loose connections again