CH not working unless HW is also on.

[Fester n Rot]

I have just found this great forum while searching the web for answers.

We have recently moved house, and i have noticed that when i set the timer (Drayton TEMPUS 7)for CH nothing gets warm. If i set the HW and CH to come on at the same time all seems okay.

We have a gravity fed system with an expansion tank in the loft, and a HW tank in the airing cupboard, with the pump, and a 3 way valve. The boiler is a BAXI solo 2 PF.

Our old house had a combi system, so this is all new to me.

Is this normal? and if so, why?

Thanks.

 

[Rob]

The 3 port valve probably isnt wired correctly...

Any good with live electrics and a proper tester?

 

[Fester n Rot]

I am quite good (electronics engineer).

So is it as i thought, that you should be able to put the CH on, without the HW?

Any suggestions?

 

[MANDATE]

Agree it may never have been wired correctly. if the valve is to move beyond mid point, it totally depends on the grey wire going into the valve to be live, . When you identify the grey in the terminal box there should be two wires connecting to it. One comes from the satisfied terminal of the cylinder stat and the other comes from the HW OFF terminal on the programmer.
On the other hand the valve head has two micro switches. If first micro switch is faulty and does not pick up the power off the live grey wire, then again it will not go beyond mid point. Or it may be ok and it does go to the CH position, but if the second micro switch is faulty there will be no power output from the valves orange wire to fire the boiler.
Also it could be down to the synchron motor which has to drive the quadrant against a spring.
May I suggest you read other posts on this subject ' 3 port mid position valves'.
1st job check wiring 'see honeywell site' it's a 'Y' plan

 

[MANDATE]

Oh forgot to say Yes you can have CH only. Also when you have HW and CH together, it is only until one side gets satisfied, then the valve moves to either HW only or CH only until the demand changes.
Also power to light boiler comes from valves orange wire in the case of CH only. In the case of HW only or HW with CH power comes from cylinder stat. This explains why you get CH with HW but not CH only.
Cause nothing coming from orange wire. why? wiring? motor? micro switches?

 

[Fester n Rot]

I have been checking the wires/colours in the whole sytem to see what goes where, and there is no HW OFF wire connected to the programmer.

There is only a red wire connected to the HW ON terminal, and a Yellow wire connected to the CH ON terminal.

I have printed the Honeywell diagram, and that too has an HW OFF wire shown.

Could this be my problem?

The 3 port valve is a British Gas BGMVSP-23 if that is any help.

 

[MANDATE]

I don't know of the valve in question but they all work on the same principle.
The HW ON wire should go to cylinder stat (input).then there are two output wires, one to fire boiler which switches to feed the grey of valve when HW is satified
The yellow from CH on should go to room stat and then from room stat it joins the white wire of valve.
When CH is required alone the grey wire is what drives the motor forward over the last half of the range. It is only applicable when there is either (a)no demand for HW, or (b) there is a demand but it has been satisfied.
(a) is catered for by a wire from the HW OFF terminal and (b) is catered for by a wire fro the satisfied terminal of the room stat. both these wires linkint to the grey wire of valve. (in the terminal box or the link could be made at the cylinder stat.
With no wire from HW OFF it cannot supply power to the grey wire so cannot operate when HW is in fact off. so yes this is the problem.
Also better make sure the wire between stat and grey of valve is also present.

 

[Fester n Rot]

Hmmm, i think i may connect it up and see what happens.

I have been checking the diagram you recommended, and all else seems okay, but i have noticed that my BAXI solo 2 PF boiler has a Live feed for a pump, and also a SL (switched live) to fire the boiler ( i presume).

The diagram only shows the boiler with one live, does this explain why my pump connection is on a seperate terminal?

Your help is appreciated. Wife thinks i'm going mad, all she's seen is my ass sticking out the airing cupboard for last few hours...lol

 

[Fester n Rot]

I have connected a wire between HW OFF on the programmer and the orange wire, and everything seems to be working perfectly.

I have tested that cyl stat, and room stat, control, and they do.

The 3 way valve moves to the position you expect also.

I've got to say a big thank you to everyone that helped, it was much appreciated.

I've asked the neighbour how theirs work, and its CH only with HW on!!! Redrow homes.....whats betting all the estate is the same with a wire missing from HW OFF?

Anyone know why the boiler has two lives, as posted previously?

Thanks.

 

[MANDATE]

The wire from the HW OFF terminal connects to the grey wire of the valve not the orange.
The grey wire (if it's live) takes over when the power through the white wire is cut off by micro switch at mid point to drive the motor forward.
The boiler stops receiving power from the cylinder stat if HW is satisfied or been turned off.
Due to valve movement over second half of range a second micro switch is triggered so the orange wire becomes live and feeds power to the boiler. You'll find the boiler stops and restarts again due to this switch over.
The power to feed the output of the orange comes from the white wire which in turn comes from the room stat, so if you have connected HW OFF direct to the orange, then there is no control of the heating by the room stat.

 

[twgas]

should in fact have three lives to boiler
permanant live, obviously connected directly to supply
switched live, recieves power from orange wire on valve to turn boiler on
pump live, actually sends power from boiler to pump. If boiler is still hot when ademand is cut the pump overrun kicks in, which gets its power from perm live and sends 240v to pump live, running pump to dissipate heat from boiler.

 

[Fester n Rot]

LOL... My mistake, i've just been and checked i did connect HW off to the grey wire, I must of just typed Orange.

The wiring is that much of a rats nest its done my head in.

Yes, there are actually 3 lives, but i was only counting control wires. It was the honeywell diagram i was following that only shows one L wire. You are correct, there is a pump L that is on a seperate terminal, and then a SL that controls the firing of the boiler. I guessed it was because when the boiler shuts off, the pump seems to run for 5 mins or so after.

Sytem has been working perfectly for last couple of days, and i can now change the programmer because i don't need the HW on all the time the CH is on. I have taken off 36 hours over the weeks program from the HW program......that must save a fortune in gas!!!

Thank you all so very much for your help.

 

[Agile]

LOL...
The wiring is that much of a rats nest its done my head in.

As an electronics engineer it should have been normal business!

Just as well you are not checking the wiring on that wheelless Boeing at LHR !!!

Tony