No heating without hot water

[Fordy81]

So basically we moved into this house a few months ago and have just found out we can't get the central heating to work unless the hot water is on!

We have an unvented system, hot water tank & pump & 3 port valve in airing cupboard, F&E tank in loft, control panel/programmer, and a thermostat.

If the room thermostat has the flame and CH is on at the programmer, nothing happens. Boiler doesn't fire up. No errors or anything.

Hot water works fine when requested.

If HW is on, then CH will also come on. The 3 port valve A side pipes get hot if CH is requested, and they cool down when thermostat turned down to not request heating. I don't know if this rules out the 3 port valve but the rads will get hot doing this. But if I then turn HW off, leaving CH on, it stops working.

I have changed the motorised part of the 3 port valve but without solving the problem.

Any ideas please?

*The grey wire that is 'loose' came from the very left hand terminal where the single earth is

 

[ianmcd]

sounds like it is wired wrong, if wired correctly HW on and HW thermostat calling valve should be at port B, with no HW demand and CH demand valve should be at port A, with a demand for both valve should be in mid position

 

[Fordy81]

sounds like it is wired wrong, if wired correctly HW on and HW thermostat calling valve should be at port B, with no HW demand and CH demand valve should be at port A, with a demand for both valve should be in mid position

Is there any way of telling that from the attached picture in my first post?

 

[ianmcd]

Is there any way of telling that from the attached picture in my first post?

Yep as suspected the grey wire from yout mid position valve is not connected to anything, this is the HW off wire and the system will not work correctlt unless it is correctly wired

 

[Fordy81]

Yep as suspected the grey wire from yout mid position valve is not connected to anything, this is the HW off wire and the system will not work correctlt unless it is correctly wired

Ahh sorry, I should have pointed out my edit. This wire came from the very left hand connector (where the single earth is), I took a picture after I'd taken it out. This was connected, and is now again

 

[ianmcd]

Never trust colours of wires in a heating system , if that had been an earth it would trip your electrics if wired correctly the grey wire should go into a connection with two other wires, HW off from Programmer and HW satisfied from Cyl thermostat, it is wired incorrectly

 

[Fordy81]

Never trust colours of wires in a heating system , if that had been an earth it would trip your electrics if wired correctly the grey wire should go into a connection with two other wires, HW off from Programmer and HW satisfied from Cyl thermostat, it is wired incorrectly

I did wonder if it was earth. It didn't make sense to me.

Thanks for that. So what would that green/yellow be? Is it right it being on it's own?

 

[Fordy81]

I meant to post this picture too. There was a broken orange cable end still attached. There is no 'loose' orange wire so to speak anywhere. God knows why it was left there.

 

[Fordy81]

So I moved the grey wire to what I believed to be the correct slot, HW off and HW satisfied. From the process of elimination I went to the wire from the cyclinder stat that was only connected to one other.

This still didn't fire up the boiler when requesting CH only. However, if I requested HW the boiler would fire up as normal, then put CH on, then turn of HW, the boiler would stay on for CH. It didn't do that before. If turning the room stat down to turn the flame off, the boiler would go off. However turning it back to request CH, it wouldn't restart.

Does sound like the whole wiring is in a right pickle but I don't know where to begin. At a guess, there's a problem with CH on wire???

 

[ericmark]

From memory the tank thermostat has three connections as well as earth, this is typical

the boiler and pump are either from orange wire from motorised valve or room thermostat and tank stat this

shows how valve works and Y plan here

 

[Fordy81]

Are wire colours standardised? So they will all do the same thing regardless of make? I have an old Potterton EP2002 programmer if that helps. I just can't figure out what wire is doing what and what it should be connected to!

 

[ianmcd]

No wire colours in CH systems mean absolutely nothing, the only wires that you can rely on by colour are the ones from the mid position valve they will be the same colour as in the installation instructions for the valve, the others are a lottery

 

[stem]

The grey wire from the motorised valve should go to the EP2002 terminal (1) HW OFF

......and also to the satisfied terminal of the hot water cylinder thermostat.

This wire is responsible for moving the 3-port valve to the 'central heating only position', and it keeps the heating going when the hot water goes off.

 

[Fordy81]

Update: So, I managed to break the programmer trying to get it off the wall. It had been grouted on. So we were without heating for 8 days while waiting for a plumber. In that time the immersion also packed up but got that fixed within a couple of days. Two oil rads kept us going heating wise.

Turns out there weren't enough wires for all the commands so CH ON or maybe HW OFF on it's own was sacrificed (think that's what the plumber said) so they used that wire for an earth. Whether the wire has gone missing at a junction box under the floorboards or not, I don't know. So long story short, he ran another wire along the top of the wall for us and up in to the airing cupboard with enough slack for us to bury it when we get round to doing the kitchen. As luck would have it there was a hole for an old coaxial that went straight in so that made it easier. Hooked up now with Nest, new cylinder stat and new immersion heater.

Thanks for all the help