Boiler installation advice please - why two?

[Gingerbread Man]

Advantages of hopefully (!) always having one working boiler if one of the two boilers fails.

Quite often setup where one's main role is the hot water and the others is primarily heating, but the hot water boiler can chime in to work with the second to help with the heating if needs be. Heating up the house quicker in the depths of winter.

You can also run on one out of the two boilers for example in the summer where you don't need such a big heat output - hot water only and central heating turned off. Saves one big boiler firing up to only heat a cylinder.

Edited by Gingerbread Man on Wednesday 26th September 18:38

[Deva Link]

How big is the house?

[motco]

Deva Link said:

How big is the house?

Thanks GBman

House size not easy to answer as it's technically a bungalow of c.1550 sq ft but has a full area basement (it's on a steep hillside and one end of the basement is underground) and garage of another 1600 sq ft in all but the garage isn't heated and the basement only sparsely heated. I don't know what output the installer was aiming at and the estate agent knows less than I do. Sadly the elderly widow owner went on holiday and didn't survive the experience so I cannot ask her who was her heating man.

[Deva Link]

motco said:

House size not easy to answer as it's technically a bungalow of c.1550 sq ft

That's a good size all on one level.

Perhaps, as suggested above, it was done with some thought for when the the full output of a large boiler wouldn't be needed.

Who knows what the reason is though - could be the installer had a couple of boilers going cheap, or the occupier was nervous and wanted a back-up.

[Gingerbread Man]

Quite a common install for two smaller boilers instead of one big boiler.

[897sma]

It used to be more common on older systems in larger properties to give you more flexibilty and lower running costs as the 2nd boiler would only kick in on colder days as demand was needed. Modern boilers are much more efficient at modulating their burners and replacing those two with a new much more efficient new one would probably pay for itself in 3 years.

[Deva Link]

motco said:

However, for some reason there are two apparently in parallel with a motorised valve between the two on the outflow side.

I'm just an interested amateur, but the pipe diameters look like 22mm and I wonder if they could carry the heat of both boilers running flat out?

Wild guess, but maybe it's been done like that to give the system (which must be fairly large) a bit a kick when starting from cold and then it drops back to one boiler once it's up to temp?

[Martyn D]

Looks unusual and "interesting"!
The zone valve is on the return, do you know what opens it up and does the boiler fire up with this zone valve in the closed position?
Is it a sealed system with an expansion vessel?
Others may disagree but if it was in my house it would need some attention!

[motco]

Martyn D said:

Looks unusual and "interesting"!
The zone valve is on the return, do you know what opens it up and does the boiler fire up with this zone valve in the closed position?
Is it a sealed system with an expansion vessel?
Others may disagree but if it was in my house it would need some attention!

I know very little about it but I am getting a full survey done soon and I hope to get access while that's going on so I can give it a look over. I cannot confirm whether the valve is on flow or return as I don't know the boiler schematic.

[fourpointsixgt]

The zone valve will open and the l/h boiler fires up, therefore the r/h boiler will be hot water and be used all year round and t'other one comes on for the heating. I reckon!!!
BTW the boilers are Potterton profiles, now obsolete, but generally reliable.

[motco]

fourpointsixgt said:

The zone valve will open and the l/h boiler fires up, therefore the r/h boiler will be hot water and be used all year round and t'other one comes on for the heating. I reckon!!!
BTW the boilers are Potterton profiles, now obsolete, but generally reliable.

Many thanks fourpointsixgt and everyone. The surveyor is on site on Monday and I will try to get in there while he's there to look more carefully. Glad the boilers are generally okay - my old Potterton floor standing one is more than 40 years old and still works well!