Central heating wiring

[jgh]

As part of putting this shower in, I had to disconnect the central heating controller to rethread the wiring. I carefully noted down what colour wire went where in the wiring box. On coming to connect it back up, I discover it has two black wires, and I've only got notes for one! Where've I gone wrong? This is what my notes tell me:

(use monospace)

E---(3)

N---(2)---------------+---------------+--------------------+ | | | r r b | | | L---(1)---+---TIMER---+ | | | g b |y r r b | | o--------(5)-----ROOMSTAT---(6)---VALVE---+ +---o\ | |g | | \o | | | | | (3) | +---------+ | | o--+ | | +---o\ k | | | \o----------- | | | k ? ? ? - - - -+ | +------------------ | | b r r b | +---BOILER-------(4)-----PUMP-----+ | |y |g | | (3) (3) | +---------------------------------|

Something's clearly wrong as there's no supply to the boiler and pump.

The controller is a 24-hour Honeywell ST699. Valve is a two-pipe (in/out, not three-way) Boiler is an old glowworm.

SUPPLY: R-->1 B-->2 G-->3 PUMP: R-->4 B-->2 G-->3 VALVE: R-->6 B-->2 G-->3 RMSTAT: R-->6 B-->5 Y-->2 BOILER: R-->4 B-->2 Y-->3 CNTRL: R-->1 B-->2 G-->5 K-->6 K-->?

Thanks in advance for any help.

-- JGH

[jgh]

Sorry, didn't label the controller switches:

As part of putting this shower in, I had to disconnect the central heating controller to rethread the wiring. I carefully noted down what colour wire went where in the wiring box. On coming to connect it back up, I discover it has two black wires, and I've only got notes for one! Where've I gone wrong? This is what my notes tell me:

(use monospace)

E---(3)

N---(2)---------------+---------------+--------------------+ | | | r r b | | | L---(1)---+---TIMER---+ | | | g b |y r r b | | o--------(5)-----ROOMSTAT---(6)---VALVE---+ CH +---o\ | |g | | \o | | | | | (3) | +---------+ | | o--+ | | HW +---o\ k | | | \o----------- | | | k ? ? ? - - - -+ | +------------------ | | b r r b | +---BOILER-------(4)-----PUMP-----+ | |y |g | | (3) (3) | +---------------------------------|

Something's clearly wrong as there's no supply to the boiler and pump.

The controller is a 24-hour Honeywell ST699. Valve is a two-pipe (in/out, not three-way) Boiler is an old glowworm.

SUPPLY: R-->1 B-->2 G-->3 PUMP: R-->4 B-->2 G-->3 VALVE: R-->6 B-->2 G-->3 RMSTAT: R-->6 B-->5 Y-->2 BOILER: R-->4 B-->2 Y-->3 CNTRL: R-->1 B-->2 G-->5 K-->6 K-->?

Thanks in advance for any help.

-- JGH

[Peter Andrews]

Sorry can't really make out what might be wrong from your diagram - too many inconsistences! However look at

there are several diagrams and you should be able to work out what is wrong.

Peter

[Roger Mills]

Ditto. If you've got only one valve, and it's a 2-port jobby (as opposed to

3 port) you've probably got a C-Plan system. If so, there will be 4 pipes connected to the boiler - 2 for a gravity circulation HW system and 2 for a pumped CH system. Can you identify with that?

If so, have a close look at the C-Plan wiring diagram shown in the above Honeywell reference, and make sure that your wiring conforms with that.

Cheers, Roger ______ Email address maintained for newsgroup use only, and not regularly monitored.. Messages sent to it may not be read for several weeks. PLEASE REPLY TO NEWSGROUP!

[jgh]

No, there's only two water pipes connected to the boiler - heating flow and heating return. I believe it's pumped hot water/pumped heating. The pipework is as follows:

vent feed | | +---+ | | +---------------+ +--PUMP-+-VALVE---+---+---+---+- | | | | | | | +----+ | | | | BOILER tap HWC rads | +----+ | | | | | | | | | | +---------------------------+---------+---+---+---+-

-- JGH

[jgh]

This looks electrically correct. Comments before I wire it up?

E---(3)

N---(2)---------------+---------------+--------------------+ | | | r r b | | | L---(1)---+---TIMER---+ | | | g b |y r r b | | o--------(5)-----ROOMSTAT---(6)---VALVE---+ CH +---o\ | |g | | \o | | | | | (3) | +---------+ | | o--+ | | HW +---o\ k | | | \o------------ - - - - - - - -+ | | k | +------------------- - - - - - - + | | | | r b | (4)-+----PUMP----+ | |g | | (3) | | r b | +---BOILER---+ |y (3)

One of the black wires from the controller is the (6) connection I had written down, and the other goes to (4) to feed the pump and the boiler.

When the CH switch is on, then the roomstat turns on the valve (enables rads), pump (pushes water) and boiler (heats water) all in parallel.

When the CH switch is off, then if the HW switch comes on then the pump and boiler come on, regardless of the roomstat, but the valve stays off, so no heat gets to the rads.

-- JGH

[Roger Mills]

OK, so you've got a pretty peculiar setup - which doesn't correspond to any of the standard 'plans'. As far as I can see, there's nothing to control the temperature of the DHW - so it will get scalding hot when the CH is running full chat, and no boiler interlock to turn off the boiler (and pump) when all demands are satisfied.

It would be a piece of cake to convert it to a Y-Plan system - which would give truly independent control of CH and HW *and* provide a boiler interlock. All you need is to get rid of the corrent 2-port valve, and put a

3-port mid-position valve just after the pump at the point where the CH and HW circuits split. Add a cylinder stat to the hot water cylinder, and wire it all up as per the Honeywell Y-Plan wiring diagram, and Bob's your uncle!

[jgh]

Looks the same as my mum's house, my grandma's house, my nanan's house, my great-uncle's house... Might be peculiar to Sheffield.

The thermostat within the boiler inside the inspection cover? If the boiler stat goes open circuit because the flow is too hot, then the pump (in parallel) will keep the flow circulating, dropping the temperature.

Almost all of the standard plans I've seen on the 'net have a cylinder stat, which my system doesn't have, unless the boiler stat is my system's equivalent. It would perform the same switching function.

No, I just want to reconnect the control system so's I can have a shower, do some washing up, and have a warm house! It uses to work perfectly until I made the mistake of thinking it would be a piece of cake to rethread the cable.

-- JGH

[Roger Mills]

The problem with that is that you can only run the boiler at the temperature at which you want the DHW - about 60 degC - anything above that, and you'll be in danger of getting scalded. HOWEVER, in the winter, you are likely to need a flow temperature to the radiators of 80 degC or more - which you cannot possibly achieve if the boiler stat is set to 60!

With a proper control system you can cut off the flow to the cylinder once that gets up to the desired temperature, whilst continuing to heat the radiators. You can also shut down the boiler altogether once both the HW and CH demands have been met. As far as I can see, you run the boiler and pump continuously during the timed period - so you waste a lot of energy keeping the boiler hot when it doesn't need to be.

[cj]

Hi Remember it well from the 70's refurb era here in the NW

2 pipe fully pumped with no tank stat used the boiler stat to regulate water temp. Comes nowhere close to modern reg's but still works.

Can't unserstand your ascii art (sorry) but wiring was prety simple.

2port vave controling c/h through room stat programmer controlling boiler/pump Usually a randal timeclock used with hw only or hw/ch switch This meant you could not have just the c/h on but hey in the 70's ppl were glad to have any heating . Wiring was :- (nb although not listed all earths are joined) Mains live & neutral to programmer Boiler pump and motorised valve neutrals to neutral (all 4 neutrals joined) Boiler & pump live to programmer HW Roomstat feed to programmer CH Roomstat return in connector block to motorised valve live.

Basically the clock powers the pump & boiler in HW mode and Pump boiler motorised valve (through roomstat) in CH/HW mode.

Still some of these systems working here in Gtr Mcr with the old Glow worm boilers. Not the IDEAL way to wire a system but in those days it worked (and still does).

HTH

CJ

[jgh]

Did you display it in fixed text? Courier, System, Monospace, etc.

Great, thanks. All I need atm is to turn the existing system back on again, I'm not in the position of being able to replace anything. Replacing the boiler may be next year's project, and then I'll pay somebody to do it. It's been a big enough job just putting this shower in! :)

-- JGH

[jgh]

For reference (as I can't find this type of system described anywhere on the web) I've put the wiring and plumbing diagram on my site at

are welcome to copy it.

-- JGH

[cj]

Hi JGH FYI all the systems we dealt with had the pump in the return leg this (so the plumbers told me) was to stop over-pumping the wiring was from the glow-worm range fitting manual of the day and was headed Std fully pumped wiring ( IIRC) . Weekends coming so will trawl my old logs etc and repost if I find anything.

CJ

[Roger Mills]

That system was only a very small step up from the alternative (at the time) 'standard' of gravity HW and pumped CH, the only difference being that HW was also pumped - plus you saved a bit of pipe (but needed a motorised valve). This and the gravity HW arrangement *both* suffered from the fundamental disadvantages of:

• not being able to have CH without HW

• not providing a boiler interlock

• having no control of HW temperature, other than via the boiler stat - which, if set at the right level for HW, would be too cool for CH

I can't imagine why anyone would want to perpetuate such a system in this day and age, when it would be so easy to convert it to Y-Plan (or even S-Plan) and do away with all the above problems at a single stroke.