Wiring centre for central heating & hot water

[EngineerJack]

I wonder if anyone can advise. I'm a bit perplexed by this one....

A few years ago I had a new central heating boiler installed. The system comprises of a boiler, with 2 external pumps for the heating (one for upstairs, one for downstairs) each with a 2-port valve and another external pump for the HW (on the return pipe, no valve, gravity fed).

I've been looking at replacing the robust wiring centre as currently I can only get HW when the heating is on... which is fine in winter but in the summer it is a bit of an issue.

I've been looking at S-Plan wiring centres, but they only seem to support 1 pump.

How easy (or difficult!) would it be to use a standard S-Plan wiring diagram but extend it to accommodate the 3 pumps? I also have a 3 channel programmer (not in use yet) which should be able to allow me to put either/both CH zone on or HW only - or all 3. Ideally I need to be able to heat the water in summer without pumping CH round too.

I have one room stat and a cylinder stat.

I hope that makes sense. And I know it is difficult without diagrams.

Can anyone help?

Best regards,
Jack

 

[martin43]

Hi Jack

There is a contradiction in your post. You state the HW is gravity fed yet it has it's own pump! In principle the concept of S plan wiring can be extended to as many zones as you wish, but what you don't mention is whether the HW part is also the feed and expansion for an open vent system. I suspect it probably is which makes converting it to fully S plan problematic.The best solution if it is currently open vent is to convert it to a sealed unvented system whence the HW becomes just another zone, but you would need a suitable unvented HW cylinder installed.Two questions, do you have a small cistern in the loft for your CH system and is your HW cylinder a traditional copper unit with either a red heat jacket or green foam insulation? Pics would be really good.

Regards
Martin

 

[EFLImpudence]

Have you got that right?

You don't have a pump on gravity DHW system - hence the gravity. (or vice versa).

How come only one room stat with two-zone heating?

 

[AndyPRK]

Best bet is to figure out why you can't get hw on its own. This is likely to be easier than ripping everything out and making things worse.

I would guess nothing is commanding the boiler on.

You probably require a relay.
Timer hw out to hw stat, then to hw pump and relay coil.
Relay contact between live and boiler. (Same as orange and grey wires on valves)

I expect it was gravity hw with a pump added later.

 

[ericmark]

It depends on what micro switches are inside the motorised valves

I did this some time back for some one who wanted zones there are four micro switches used in this version which are fitted inside the motorised valves. You could in theroy used relays but there would need to be a timer to delay the relays as with the motorised valve the boiler is only switched on after the valve has opened. So you may need to change the motorised valve heads to get the micro switches required.

 

[EngineerJack]

Thank you everyone for the replies.

Yes the valves are Honeywell 4043 valves with 6 wires.

There is a header tank in the loft. One for hw and one for ch. Both are unsealed systems. Gravity fed, with pump on the return pipe of hw.

Cylinder has a green jacket. Primatic system I think.

Boiler receives a single switched live and also has pump overrun. I was considering controlling overrun from a time delay relay in the wiring centre so simplify pump control.

Jack.

 

[Taylortwocities]

Just a simple thing to check. Some programmers have an option switch that tie the heating and hot water together for the old-style gravity systems.
With these yoou can only get HW when heating is on.

Check is your programmer has actually got the gravity option disabled.

 

[AndyPRK]

Just a simple thing to check. Some programmers have an option switch that tie the heating and hot water together for the old-style gravity systems.
With these yoou can only get HW when heating is on.

Check is your programmer has actually got the gravity option disabled.

The symptom you would get in this case is no CH unless the HW was on.

Good thought though.

 

[ericmark]

Just a simple thing to check. Some programmers have an option switch that tie the heating and hot water together for the old-style gravity systems.
With these you can only get HW when heating is on.

Check is your programmer has actually got the gravity option disabled.

I thought it was reverse you can't have heating without hot water, but you can have hot water without central heating. Also the valves normally have a manual lever to allow bleeding, I have come across it where the fault was the valves had been left latched so central heating would not turn off.

 

[oldbutnotdead]

Sounds like an odd setup (or a very large house)- 2 pumps on the heating circuit and only one thermostat. Ho hum...

Also sounds as if the hot water cylinder has been set up as the overrun heatsink for the system- no valve on it and best leaving it that way.

Current wiring- the room stat should (when calling for heat) energize the 2 port valves. When the valves are open, the internal microswitches should complete the circuit firing the pump(s) and sending power to the gas valve in the boiler.

The cylinder stat (in the absence of a valve) should energise the DHW pump and the gas valve.

Each timeclock should (when active) supply the live feed to the relevant thermostat.

You don't really need a 'wiring centre' to make this work- what you do need is a circuit diagram and an adaptable box with a lot of terminal block in it- cheaper and easier, you can get a lot of box for £10.

It is possible that your timeclock is not set up (or not capable) of energising hot water without energising the heating circuit- had the same problem 25 years ago, ended up using 3 separate timeclocks (downstairs, upstairs, hot water). And then about 10 years later replaced downstairs and upstairs with wireless thermostat/controllers- much handier- wake up- ooh its a bit nippy, prod the button on the thermostat by the bed, 30 mins later nice and warm.

Very much a control problem, no need to change from vented to unvented. Curious about 3 pumps though....... because of your multiple pumps you will need some relays in the system, without them you'll end up firing all 3 pumps whenever 1 circuit calls for heat. EDIT Which is probably why you can't currently have hot water without heating. If you want a wiring diagram I'll do one but at the moment the vodka is kicking in....

 

[EngineerJack]

Thank you. That's exactly the setup. I have a single 24h timer that fires the lot up. I have a 3 zone programmer which in yet to wire in. This will give me the 3 independent timers you described.

3 pumps because the house is has long runs from end to end. Boiler is at one end.

A wiring diagram would be ideal. That's all I require to get his moving. Multiple relays is the way to go I reckon.

Jack.

 

[oldbutnotdead]

Right, try that- it isn't really optimised for getting all the wiring back to your central point but that's how it should work.

The relays- anything with 240v coil and switching 240v at minimum 1 amp will do the job. Did think about being clever and using dc through the microswitches and then diodes to prevent back linking but that would end up using 4 relays as well as a transformer.

If you only have 1 room stat then 2 heating circuits doesn't really make a lot of sense- might want to treat yourself to one of those wireless programmer/thermostats for the upstairs.

EDIT 2- how foolish of me. The thermostats should be between the timeclock and valves (in the heating circuits) and the relay (hot water circuit). DOH!

EDIT- NB Just reread your original post regarding the boiler having pump overrun. How is that working at the moment- is there a separate permanent live to the boiler and thence to one of the pumps as well as the switched live from the thermostats/valves etc. Whatever, for safety purposes that feature will need to be replicated otherwise you could get the heat exchanger overheating which wouldn't be good. It would be wise to keep the manufacturers' overrun controls- there may be additional interlocks in the system for safety purposes.

 

[EFLImpudence]

Isn't there something fundamentally wrong with this set up?

Surely, with separate pumps for each zone, the valves aren't necessary.

If the pumps are energised by the boiler for overrun, then the relays can be wired to only energise the relevant pump

 

[Spark123]

You'd think not but sometimes you get convection causing some of the radiators to heat up without that zone being on.

 

[Echo the husky]

That won't work. If say 2 zones are on, when one is no longer calling the relay will be latched on by the other zone. You must take the live in to the relays contacts from the supply not from the switching circuit. I don't know how the system is meant to operate so I can't comment further than that.