Electrical Wiring to Awkward Condensing Boiler

[superstardeejay]

Hi folks, hope someone can help us here, I'm struggling to get my head around a complicated electrical install of boiler & cylinders. I'm an electrician, not a plumber.

The new system has been installed by others but we've been called in to 'sort it out' after the previous people gave up.

Installation consists single sealed circuit gas boiler, Keston C55 with inbuilt pump, permanent & switched live supplies, auto-pump exercise and over-run.

Two Telford Stainless mains pressure DHW cyls, heating loops in parallel and fed off single NC motorized valve from boiler, each with twin built-in stats with volt free contacts, ie one for control and one for overtemp. Expansion spheres fitted.

Two Grundfos pumps external to boiler, each with motorized 2 port NC valves and feeding upstairs and downstairs rads respectively. Two Honeywell bimetallic roomstats, up and down.

Salus 2-channel timeclock with seperate volt free changeover relays for DHW and CH, operate independently through the programme.

All rads fitted with thermostatic valves.




Although it first sounded simple to me, I cant see how to get around the fact that:

1. The mains DHW cyl stats need by law to have overall control of the valve feeding them from the boiler, yet the boiler needs an open circuit at switch-off for pump over-run, anti-kettling and pump exercise reasons.

2. The upstairs and downstairs rads are fed via pump/valve combination so my previous point applies likewise.

3. The user wants the option of selecting via the timeclock either CH, DHW or both or neither, at will.

4. The boiler inbuilt pump is powerful enough to circulate water through any open valves and into the radiators or cylinders unless the respective valve is closed.


Can I wire this up to cover all senarios without doing damage either due to the boiler pumping against a closed circuit or overheating the cylinders?

Thanks and sorry for the rambling.

kev

 

[Jason.S]

Hi Kev,

If the lads cant help you here, which im sure they can, you can always try the Sparky forum:

Electricians Forum | Electrical Forum | An electrical forum for electricians in the UK - Powered by vBulletin

 

[Plouasne]

Hi folks, hope someone can help us here, I'm struggling to get my head around a complicated electrical install of boiler & cylinders. I'm an electrician, not a plumber.

The new system has been installed by others but we've been called in to 'sort it out' after the previous people gave up.

Installation consists single sealed circuit gas boiler, Keston C55 with inbuilt pump, permanent & switched live supplies, auto-pump exercise and over-run.

Two Telford Stainless mains pressure DHW cyls, heating loops in parallel and fed off single NC motorized valve from boiler, each with twin built-in stats with volt free contacts, ie one for control and one for overtemp. Expansion spheres fitted.

Two Grundfos pumps external to boiler, each with motorized 2 port NC valves and feeding upstairs and downstairs rads respectively. Two Honeywell bimetallic roomstats, up and down.

Salus 2-channel timeclock with seperate volt free changeover relays for DHW and CH, operate independently through the programme.

All rads fitted with thermostatic valves.




Although it first sounded simple to me, I cant see how to get around the fact that:

1. The mains DHW cyl stats need by law to have overall control of the valve feeding them from the boiler, yet the boiler needs an open circuit at switch-off for pump over-run, anti-kettling and pump exercise reasons.

2. The upstairs and downstairs rads are fed via pump/valve combination so my previous point applies likewise.

3. The user wants the option of selecting via the timeclock either CH, DHW or both or neither, at will.

4. The boiler inbuilt pump is powerful enough to circulate water through any open valves and into the radiators or cylinders unless the respective valve is closed.


Can I wire this up to cover all senarios without doing damage either due to the boiler pumping against a closed circuit or overheating the cylinders?

Thanks and sorry for the rambling.

kev

A bit difficult to get my head around, but where is the adjustable by-pass valve, so that the pump can kick in when it needs to, and the by-pass valve allows a certain flow of water between flow and return, when every thing else is closed

 

[david williams]

poor design,who designed it,had a lot of this sort of thing lately

 

[stevetheplumber]

always hard to get your head around something like this on paper from what youve said it does sound like you need a bypass installed
the wiring can be carried out like a normal 2 zone s plan with one stat interupting the feed to the apropriate heating zone vavle . The two hot water valves wire together and use the overheat stats to cut the live feed(NORMALLY THE ORANGE WIRE ) back to the boilers. with two cylinder you will have to run in and out in and out of each stat so that either triping will cut the power to the boiler
Probably not explained very tecnmically but hope it helps
just to make it more difficult you may find the load with three pumps will exceed a normal timeclocks capabilities and will either need a higher rated clock or relays .some larger pumps have relays inside

 

[migoplumber]

on point 1, like steve says, the valves to the dhw open and close from the boiler circuit, if using a honeywell valve, then orange is the switch wire, i tend to use orange and brown together, with the blue as neutral. the regs state that the valve has to be self closing or spring loaded to shut off circulation to cylinder.

the boiler primary will always need a circulation circuit, hence use of a bypass circuit in case of closed dhw and no requirement for heating, fitting a by-pass valve sorts this.

thats as much as i can help from your description. im sure as jason says on sparky forum there will be them sparks out there that can do your installation in 5 mins with their eyes closed. definetly worth posting there as well !!

 

[superstardeejay]

the by-pass valve allows a certain flow of water between flow and return, when every thing else is closed

This is the main problem Ive got, there isnt one!

with two cylinder you will have to run in and out in and out of each stat so that either triping will cut the power to the boiler

Yes, the cyl stats were originally in parallel so that both had to trip before the flow valve to the cyls closed..meaning that one could potentially overheat! The trouble is that now, if say the family bath drains one cylinder, it won't reheat until the ensuite bath cools its adjacent cylinder and trips both heat loops back in! Really, the dual cylinders needed a valve each I suppose; indeed I found a 'spare' motorised valve shoved in a cupboard along with the remnants of the Telford install kit.

I'm beginning to think that the cheapjack plumber and his sidekick spark have alot to answer for; this is a 3-storey luxury house with 2 main bathrooms and all beds on-suite. The owners are not short of money.

 

[stevetheplumber]

i was assuming the cylinders were joined together working as one unit if im getting this right and they are in different locations or serving diferent appliances i think they should be treated as seperate circuits and possibly would be best to run a three channel timer (or a two and a single) in which case each would be controlled by its own overheat stat and seperate motorised valve

 

[doitmyself]

I've swopped thing about to make it easier to write!

Installation consists single sealed circuit gas boiler, Keston C55 with inbuilt pump, permanent & switched live supplies, auto-pump exercise and over-run.

1. The mains DHW cyl stats need by law to have overall control of the valve feeding them from the boiler, yet the boiler needs an open circuit at switch-off for pump over-run, anti-kettling and pump exercise reasons.

As there are separate zone valves on each circuit, an automatic bypass valve should be fitted. This will provide the open circuit when all zone valves are closed. It is the plumber's job to do this, if it's not done the system does not comply with regs.

Salus 2-channel timeclock with seperate volt free changeover relays for DHW and CH, operate independently through the programme.

3. The user wants the option of selecting via the timeclock either CH, DHW or both or neither, at will.

This will depend on the clock. Which Salus is it? Does he want to control the upstairs and downstairs heating zones separately? If so he will need either a three channel clock or a separate single channel clock upstairs.

There are three pumps: Internal, ground floor, 1st floor. Is it a large house? Does the system have a low loss header (see page 12 of Installation Instructions)? If not ask the installer why the two heating pumps are required? The boiler produces 40kW so the internal pump will be designed to deliver that amount of heat.

Two Telford Stainless mains pressure DHW cyls, heating loops in parallel and fed off single NC motorized valve from boiler, each with twin built-in stats with volt free contacts, ie one for control and one for overtemp. Expansion spheres fitted.

Two Grundfos pumps external to boiler, each with motorized 2 port NC valves and feeding upstairs and downstairs rads respectively. Two Honeywell bimetallic roomstats, up and down.

The boiler is ignited by supplying 230v to either SL1(heating) or SL2(hot water).

Time switch CH/HW ON to thermostat common
Thermostat call to valve brown. A call for heat will open the valve and close the auxiliary switch in the valve.
Aux switch grey wire to permanent supply
Aux switch orange wire to SL1 or SL2 (this ignites the boiler).

Presumably the two stats on each cylinder are in series (one NO the other NC), so you just treat them as one stat. The two cylinders can then be wired in parallel so either will control the boiler.

This is the main problem Ive got, there isnt one!

If there is no bypass valve, I would tell the "installer" that you won't proceed with the wiring until one is fitted!

Yes, the cyl stats were originally in parallel so that both had to trip before the flow valve to the cyls closed..meaning that one could potentially overheat!

Overlooked that in my previous reply.

The trouble is that now, if say the family bath drains one cylinder, it won't reheat until the ensuite bath cools its adjacent cylinder and trips both heat loops back in! Really, the dual cylinders needed a valve each I suppose; indeed I found a 'spare' motorised valve shoved in a cupboard along with the remnants of the Telford install kit.

Insist the "installer" put in the 'spare valve' before you wire up.

It might be worth informing the customer what is wrong and why you cannot proceed with the wiring until the plumbers "errors" have been corrected.

 

[superstardeejay]

Yep, all as I suspected but thought I'd seek a professional plumber's advice before getting back to the customer.

I've now contacted one of my old customers (who is a plumber) to come and fit a bypass and reroute the cylinder loops so they are fed independently from their own motorized valves.

The rest of the circuit I've already fitted...they hadnt even interlocked the valves so they only start their respective pumps when fully open.

As it is now, its all interlocked and wired so that everything happens when it should, except to get around the lack of bypass, I've wired the downstairs CH valve permanently open so there's not a closed circuit unless the spurbox is off. The only temporary downside is that when on DHW only, the downstairs rads get a little warm due to the internal boiler pump...it will do till the plumber can attend. They're also using the immersion heaters in the cyls as its too warm at the moment for the boiler anyhow.

Does the system have a low loss header

No, the CH is sealed via regulator and top-up tap, the DHW is mains pressure.