Leaking Pipes After Combi Boiler Installation

born_again

ListysDad said:

Firstly you must have about 15 bedrooms to need a 30kw boiler. It certainly will not be efficient to run as it seems hugely oversized. 
By the way, I'm a plumber for my sins... 

Interesting. As our Worcester Greenstar 30Si bolier is 30kW

https://www.plumbnation.co.uk/worcester-greenstar-30si-compact-combination-boiler-natural-gas-erp-10-12703?

So really interested as to your source on this, so I can go back to BG & claim compensation for a install of the wrong boiler for a 2 bed bungalow...

daveyjp

"Plumber", not gas engineer.

Combi boilers are sized based on cold water flow rates and subsequent hot water supply needs, not the number of radiators in a property.

30kw is max output, all modern combis modulate the heat output to provide the minimum amount of heat required to keep the heating circuit at the set temperature.

HHarry

As Daveyjp says combi boilers are sized to provide enough piping hot water as needed, not for the radiator heating load.  You could probably install a boiler at half the size to heat the house, but you’d potentially only get a dribble of luke warm water from the tap.

Leaking pipework, particularly radiator valves, isn’t uncommon when changing from a gravity to pressurised system.  Most companies warn about this in their T&C’s.  Boxt cover it in section 7 & 12 of theirs.

bris

Going from gravity to mains pressure is always a bit of a risk, I was going to ask if you were warned about this but it looks like you were.

As for those saying boiler size doesn't take amount of radiators into consideration well of course they do.

ComicGeek

bris said:

As for those saying boiler size doesn't take amount of radiators into consideration well of course they do.

In the context of a combi boiler for a larger house though, which is what was discussed above - I've never seen a combi boiler that has been sized on space heating requirement rather than hot water load.

born_again

ComicGeek said:

bris said:

As for those saying boiler size doesn't take amount of radiators into consideration well of course they do.

In the context of a combi boiler for a larger house though, which is what was discussed above - I've never seen a combi boiler that has been sized on space heating requirement rather than hot water load.

Same number of people living in a 2 bed house or a 5 bed will require the same water load, but will require a higher heating load. 
We could have had a 20kW boiler, but due to the number of radiators 30 was recommended by the installer.

ComicGeek

born_again said:

ComicGeek said:

bris said:

As for those saying boiler size doesn't take amount of radiators into consideration well of course they do.

In the context of a combi boiler for a larger house though, which is what was discussed above - I've never seen a combi boiler that has been sized on space heating requirement rather than hot water load.

Same number of people living in a 2 bed house or a 5 bed will require the same water load, but will require a higher heating load. 
We could have had a 20kW boiler, but due to the number of radiators 30 was recommended by the installer.

And that instantaneous hot water load from the combi will be the same regardless of number of people, and regardless of how many consecutive showers are taken. Boilers will outlast most people's home ownership, so would be a poor choice to just base boiler choice on current low occupancy of larger houses.

Your 20kW boiler wouldn't have been a combi boiler though, that's a regular boiler with cylinder.

I bet your installer just counted the number of rads rather than actually calculating the heat loss. I would put money on 30 kW space heating load being massively oversized, most installers don't have a clue about sizing.

born_again

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