Two Boilers Wiring Together

[Sharpend]

Lads bit of advice if I may.

Have a large dom property which has been refurbed. It has UFH on ground floor conventional rads on top two floors plus hot water. The plumber has said that it needs two boilers as one is not sufficient.

So wiring two together, anything I should be aware of? Wire in parallel to operate both at any one time? My concerns were if valves were closed pumps running against the closed valves?

Haven't got details from plumber as to how he has done his part as yet. I'm guessing that the boilers have internal pumps but only a guess.

Suggestions please.

 

[ProDave]

If controls are done properly the boiler(s) only fires when the valves are open.

So are both boilers plumbed in parallel so they are both heating the same thing, just two of them running together for more power?  if so just wire them together.

If it's more complex that the second one only kicks in if the demand is high then you will have to design something better.

More information from the plumber needed.

but perhaps it would be better just to spend more money on insulation rather than just extra heating for hungry building?

 

[MeFil]

How big a property is it to need two boilers....? I've seen some big houses with only one boiler.

 

[Sidewinder]

To be honest, unless there is a damn good reason, to me it sounds like the plumbit has mucked up.

For goodness sake, I've seen factories heated with one boiler, and this gives hot water as well.

Unless there a space constraints, I don't see the reason for two, unless one was already there and the end user would not pay to rip it out and fit one big boiler, TBH, it just does not make sense to me.

 

[Sharpend]

Well have spoke to plumber and boiler mfr, two boilers feeding into a low loss header, 3 channel prog, each boiler is standard system boiler with internal pump, each zone has its own valve and pump.

Require a 230v double pole relay to connect between boilers and header.

Worcester boilers 30cdi, wiring diagrams all on worcester bosch website, looks pretty straight forward.

Thanks for the input guys.

Don't know why the plumb has asked for two boilers, something to do with one may struggle to be efficient.?

 

[ProDave]

What's the "header"

Thermals store tank?

I still think unless this is Buck House, more insulation is the way forward.

 

[Sharpend]

From what the plumb described it sounds as though the header is a glorified heat loop. Basically the boilers fire up and circulate around the header, then as any of the zones call for heat the water is drawn from the header, when zones stop calling, then the header allows for the hot water to be circulated to dissipate heat from boilers .

The relay is to isolate the boilers electrically in the event of a fault.

It's an old Edwardian house. To be fair the whole of the place has basically been refurbed, probably be wise to sort so e etc wall insulation, but still!

 

[ProDave]

Sounds very ineficcient to just allow it to "circulate to dissipate heat from the boilers"

To be honest I don't have a lot of faith in the plumbit knowing what he is doing.

If the place is REALLY being refurbished then the only sensible thing with todays energy prices is to do something about the insulation AND the air tighness of the building. It can be done, and not for that much.  I have a particular interest in energy eficcient buildings (I'm designing a new passive house for myself that will require very little heat). A friend local to us has taken an old stone cottage and insulated and sealed it room by room vastly reducing it's heating needs and cost.

 

[SLIPSHOD & SLAPDASH]

Well have spoke to plumber and boiler mfr, two boilers feeding into a low loss header, 3 channel prog, each boiler is standard system boiler with internal pump, each zone has its own valve and pump.

Require a 230v double pole relay to connect between boilers and header.

Worcester boilers 30cdi, wiring diagrams all on worcester bosch website, looks pretty straight forward.

Thanks for the input guys.

Don't know why the plumb has asked for two boilers, something to do with one may struggle to be efficient.?

I have done quite a few properties like this , its a common occurrence now to have more than one boiler. Sometimes simply having the boiler stats at different settings to make one the main and one the boost is used. Other times a big control panel has been delivered. The last one i did was a 8 bed, 8 bath house with 3 large Mega-flows. The 2 boilers were to get the recovery times up on the DHW & in case of a breakdown they still had one.  I have some pics somewhere of that system.

 

[Sidewinder]

Now redundancy is a situation that I can relate to using two boilers, however, I can't follow why two boilers were "needed", the 30CDi is a small boiler, much larger are available, and with correct design a single boiler could have been used.

Which could well have been a more cost effective option for both install and on-cost.

 

[Sharpend]

Just thinking about this system. It has three zones individually pumped, is there any other ways of wiring without the use of individual relays to prevent pumps starting that haven't been called for? Normally would use the orange fire wire from valve to start pump but with three pumps the other two would start but valves remain closed, damage to the pumps would be inevitable.

 

[SLIPSHOD & SLAPDASH]

Apart from  2 jobs where a control panel was supplied i have never used any relays. Each room stat, either standard or for underfloor heating  trigger wire (normally orange) operates the valve & pump    for that area only .  There is no interconnection or backfeed in-between.  If something was to stick or go wrong both the valve and pump are still connected together so it would not burn out the pump

 

[Sharpend]

Surely if all three valve orange's and the three lives to pumps were together to the boiler trigger, wouldn't the opening of one valve trigger the boiler and subsequently the other two pumps? Which would be pumping against closed valves?

 

[NozSpark]

So why not stick the oranges through DP relays so they don't feed back.... ????

 

[SLIPSHOD & SLAPDASH]

This is how i have done it loads of times.



No relays needed. Room stats can be omitted if not needed.

I give up trying to get W8 to put pics the correct way round, Tried 5 times and it always reverts to the way it was first scanned, however it has been saved.

 

[NozSpark]

Ahh, I see

However I've only done it once on a single boiler (mine) with pumped HW and CH (2 pumps / 4 pipe boiler) controlled only by a 2 channel programmer and room stat

 

[Sharpend]

Are the pumps not starting prior to valves opening or as valves opening? Do you not risk knackerig pump if valve motor goes or valve fails to open?

Just trying to avoid expensive call outs at later date.

 

[SLIPSHOD & SLAPDASH]

Are the pumps not starting prior to valves opening or as valves opening? Do you not risk knackerig pump if valve motor goes or valve fails to open?

Just trying to avoid expensive call outs at later date.

Yes, but there is also 100 other things thst could go wrong. This way of doing it was shown on a drawing sent to me by Potterton ages ago, its always been on big jobs, loads of pipework.

 

[Sidewinder]

You wont knacker a central heating type pump if the valve fails to open.

It will just churn water in the impeller casing.

 

[apprentice87]

I am with paul on this, Just sonds to me like a bodge cos the existing boiler is too small. What is going to happen in a few years when they get the inevitable "they do not do bits for them anymore" Then they WILL have to buy two new boilers, [or one larger new one like they should be doing now....]

john..