Heating electrics diagram - can anyone explain mine?

[silve]

Hi

I'm having some difficulties with my heating. The CH will not work unless HW is also called for. I've had british gas out twice (on contract) to look at it, and twice they changed the powerhead on the Honeywell diverter valve in the airing cupboard. This seems to fix the problem but then it intermittently returns.

I thought before I call them out a third time I'd try to understand this myself. However despite some DIY electrical knowledge, these electrics seem more complex and are not obvious to me, and I can't find a diagram online that looks like it might fit my heating. Although my heating setup looks like a "Y plan" in terms of plumbing, the electrics don't match Y plan examples posted on most sites.

So, my heating/diverter problem aside...can anyone please explain to me how my heating circuit works? It doesn't help that I don't know where some of the wires come from, so maybe someone could shed some light?

This is a sketch of the junction box in the airing cupboard:

Untitled

• silve
• 19 Dec 2010
• 1

Finally - I made a few measurements with the multimeter. I'd assumed all of this was some kind of glorifed set of switches in series. But I'm not just reading 0 or 240v, I'm also seeing 130v and 50v.. etc. what's going on!?

[edit - to add these details]
* Potterton Suprima HE boiler
* Potterton EP 2000 programmer unit - black box with CH and HW slides, allows HW and no CH, or HW and CH (sliders mechanically limited). PERMANENTLY SET TO 24 hrs CH and HW because room stat has a programmer in it.
* Heatmiser root stat acting as a volt-free switch (self installed - swapped from honeywell dial stat - I think this problem independent of that but not 100% sure, another reason to check wiring before calling out british gas again). I guess that's at the end of one of those white 3 core wires?
* p.s. sorry typo on the diagram I think for the cylinder state its black for HW call (not blue as noted), and blue for HW not called, with brown common.

 

[twgas]

Where does the grey core go, it appears to be a boiler supply but also has one wire (black) which, I think, should come from the programmer.
If you remove the prog from the back plate there is a locking switch between the two sliders to allow CH without HW.

 

[Hugh Jaleak]

Have a look here, it may help: http://octaveblue.co.uk/c_heating/index.htm Also have a look on page 2 of the Central Heating FAQ's (top of index page). D.Hailsham gives a good explanation of how the mid position valve works and why you get the lower voltage readings sometimes.

 

[silve]

Hi Mick,

Thanks for your reply. I don't know where that grey core (my typo, I meant "grey 3 core") goes... is there a secondary junction box somewhere I've missed, maybe the grey and black wires within that 3 core are split in there - one to boiler, one to programmer?

I'll try to take the front off the programmer and unclip that mechanism that enables CH/HW independently. Maybe I'll see some wiring when I do that.

That orange wire coming from the diverter - is that an output from the diverter that controls the boiler? Or is it a signal driving the diverter in some way?

Cheers

 

[silve]

Thanks Hugh that's a very instructive animation of Y plan.

I see Mick's point now about that black wire in the "grey 3 core" connected to the grey on the diverter. It should be going to a programmer on HW off, right? I wonder if reality will match the diagram.

 

[twgas]

Where is the programmer in relation to the boiler?
The orange is powered from the valve when the heating is called for but the HW isn't, if the HW is calling the power comes from the cyl 'stat - the grey wire in that connection should go to the boiler switched live.

 

[snb]

someone has had a play around and got a few wires swapped around.

this is what you should have industry standard

1 live
2 neutral
3 earth
4 heating demand from programmer and link to room stat
5 room stat demand white of 3port valve
6 hw demand from programmer common from cylinder stat
7 hw off from programmer grey from 3 port term (2) of cylinder stat
8 (1) from cylinder stat switch live to boiler orange from 3 port
9 pump live from boiler


I think you have

1 earth
2 neutral
3 pump live from boiler
4 room stat demand white of 3port valve
5 heating demand from programmer and link to room stat
6 hw on from programmer
7 (1) from cylinder stat switch live to boiler orange from 3 port
8 hw off from programmer grey from 3 port term (2) of cylinder stat

i would guess that if you disconnected the cylinder stat cable in terminal 8 and then put demand for heating you find that terminal 7 (orange from 3 port should become live (240v) but it won't beacuse the syncron motor is failing/failed

 

[matt1e]

So, my heating/diverter problem aside...can anyone please explain to me how my heating circuit works? It doesn't help that I don't know where some of the wires come from, so maybe someone could shed some light?

This is a sketch of the junction box in the airing cupboard:

Untitled

• silve
• 19 Dec 2010
• 1

1 Earth
2 neutral
3 pump switched live
4 ch switched live from room stat (this is not volt free btw)
5 ch on from programmer to room stat (see quote in brackets above)
6 hot water on from programmer to cyl stat
7 hotwater call
8 hotwater satisfied

It is standard y-plan but seems to have the programmer hw off connection routed via the first 3 core (black)

Finally - I made a few measurements with the multimeter. I'd assumed all of this was some kind of glorifed set of switches in series. But I'm not just reading 0 or 240v, I'm also seeing 130v and 50v.. etc. what's going on!?

thats normal and is caused by the internal diode/resistor arrangement internal to the valve actuator

* Heatmiser root stat acting as a volt-free switch (self installed - swapped from honeywell dial stat - I think this problem independent of that but not 100% sure, another reason to check wiring before calling out british gas again). I guess that's at the end of one of those white 3 core wires?

what make you think it is volt free?
how have you connected it?
it's the 3core connected to terminals 2,4 and 5 btw

first thing to check if you have a meter is set central heating only to on
you should get the following
between
2 and 4 = 230v
2 and 7 = 230v
2 and 8 = 230v

if the voltage to 7 is missing then the fault is with the valve or actuator

Matt

edit there were 0 posts when i started writing

 

[matt1e]

That orange wire coming from the diverter - is that an output from the diverter that controls the boiler? Or is it a signal driving the diverter in some way?

Cheers

Yes its the voltage from the white connected via a microswitch that closes when the valve is in the heating only position and used to fire the boiler

 

[silve]

Thanks everyone.

It seems the wiring is as per snb's post. That black wire in the grey 3-core must be to the programmer. I can't get the front off the programmer to confirm what goes where due to tight positioning of the boiler cupboard but assume it must be so (boiler is right above the programmer).

Regarding my comment re: volt-free switch, this was a term used by Heatmiser. Their thermostat is just a switch that closes to call for heat. I tested this back in the days the system was all working ok (e.g. I put the two wires together and the boiler started).

So thanks for clearing up the wiring - the original point of the post! I tried a couple of things with this new knowledge ...

First, the new diverter valve british gas fitted is on a multi-plug - so I disconnected this completely from the system and measured some voltages. There were still many terminals reading 130v , which seemed odd as I thought with the resistors/diodes in the valve gone nothing would generate these.

But then I disconnected all but the common on the cylinder stat. Depending on the setting one side is 240v (great) but the other is 80-120v (should be zero?). I wonder if these non-zero voltages are throwing the system out somehow, as with the cylinder stat disconnected they are absent. Is it normal for a cylinder stat to read so highly on the "open" side of the switch?

With the cylinder stat disconnected (but the diverter reconnected) I tried calling for CH. I can't call for CH with no HW due to the way the programmer is rigged, but this seemed a good approximation. When I did this, the white wire went to 240v. But the orange wire was only at 130v. It should be 240v to fully drive the boiler? So I guess the diverter seems suspect - but then how can this be, the company just changed it (and I had a new motor for it 1 month ago, fitted professionally also).

 

[matt1e]

First, the new diverter valve british gas fitted is on a multi-plug - so I disconnected this completely from the system and measured some voltages. There were still many terminals reading 130v , which seemed odd as I thought with the resistors/diodes in the valve gone nothing would generate these.

you're correct they shouldn't so something is clearly amiss
which terminals are reading 130v?
and with respect to which other terminal? (terminal 2?)
try the same tests but also use terminal 1 as a reference then post results

But then I disconnected all but the common on the cylinder stat. Depending on the setting one side is 240v (great) but the other is 80-120v (should be zero?). I wonder if these non-zero voltages are throwing the system out somehow, as with the cylinder stat disconnected they are absent. Is it normal for a cylinder stat to read so highly on the "open" side of the switch?

no its not normal but explain how you are "testing" the stat, how are you disconnecting it and how are you taking the measurements?

With the cylinder stat disconnected (but the diverter reconnected) I tried calling for CH. I can't call for CH with no HW due to the way the programmer is rigged, but this seemed a good approximation. When I did this, the white wire went to 240v. But the orange wire was only at 130v. It should be 240v to fully drive the boiler? So I guess the diverter seems suspect - but then how can this be, the company just changed it (and I had a new motor for it 1 month ago, fitted professionally also).

the motor can't drive to fully open without 230v on the grey which is sourced from two places
1 HW off on the programmer ( and you cant select this and CH on at the mo)
2 the satisfied terminal on the cylinder stat so if you have disconnected this then it wont drive fully to ch so the microswitch wont make
Matt

 

[silve]

Thanks matt1e.

This morning, the CH gods are smiling and my system operates correctly despite not changing anything since my last post. However I know that this will not last, so I have made measurements of the working system below in its various states. When it fails again I will post another set of measurements to compare.

Connectors (posted by snb):-

1 earth
2 neutral
3 pump live from boiler
4 room stat demand white of 3port valve
5 heating demand from programmer and link to room stat
6 hw on from programmer
7 (1) from cylinder stat switch live to boiler orange from 3 port
8 hw off from programmer grey from 3 port term (2) of cylinder stat

All the voltages are measured from terminal 2 (common negative). I also tested from terminal 1 (earth) and these are the same. So I think the negative is good.

In cases Ex1-4 the programmer is on 24hrs calling for CH and HW. So satisfied vs. calling below mean the room (CH) or cylinder (HW) stat is on/off.

Ex1) ** HW satisfied, CH calling:

3-8. 230v

Ex2) ** HW calling, CH calling:

3-7. 230v.
8. 68v.

Ex3) ** HW satisfied, CH satisfied:

3. 0v
4. 130v
5. 230v
6. 230v
7. 130v
8. 230v

Ex4) ** HW calling, CH satisfied:

3. 230v
4. 0v
5. 230v
6. 230v
7. 230v
8. 120v


Ex5) When I turn OFF both the CH and HW at the programmer (both stats satisfied)

3. 0v
4. 130v
5. 130v
6. 230v
7. 130v
8. 230v

For Ex6. onward CH stat is satisfied
Ex6) With HW only at the programmer and HW satisfied:

3. 0v
4. 130v
5. 120v
6. 230v
7. 130v
8. 230v


Ex7) With HW only at the programmer and HW calling:

3. 230v
4. 0v
5. 70v
6. 230v
7. 230v
8. 120v

In Ex7 switching CH stat to calling takes (5) to 0v.


--

When the heating goes on the blink again I will repeat these and also try disconnecting the diverter again etc. However if I fiddle with it now its working there may be wife consequences.

In response to matt1e, when I disconnected the cylinder stat to test, I disconnected the calling and satisifed terminals and left the common connected to 240v. I changed the stat and observed the voltage on calling and satisfied wires. These were 230v / 130v or vice versa. Using terminal 2 as negative for measurements.