Can a conventional system boiler be a closed system?

NewStart · Aug 19, 2020

As per the title?

I've only ever seen domestic system/conventional system boilers with an F&E tank and combi boilers which are closed systems.

Is there any reason a system boiler cant have an expansion vessel fitted and be made a closed system?

Or

Is there any reason you couldn't install a combi with an open vent/F&E?

steadyon · Aug 19, 2020

The following applies to the UK and its regulations:
1. You can have sealed systems with combi (always sealed), system boilers or open vent boilers provided the manufacturer allows this - these days they nearly all do.
2. You can't really run a combi boiler off an F&E tank, as the pressure is unlikely to be sufficient to pressurise the system. Also, you'd lose the benefit of mains pressure hot and cold.

Last Plumber · Aug 19, 2020

You would need to consult the manufacturers installation manual for that particular boiler.
I have seen all manner of configurations over the years but the manufacturer is the place to start if you're thinking of altering or installing something.

NewStart · Aug 19, 2020

steadyon said:
The following applies to the UK and its regulations:
1. You can have sealed systems with combi (always sealed), system boilers or open vent boilers provided the manufacturer allows this - these days they nearly all do.
2. You can't really run a combi boiler off an F&E tank, as the pressure is unlikely to be sufficient to pressurise the system. Also, you'd lose the benefit of mains pressure hot and cold.

Hadn't thought of the system pressure, that makes sense with a combi.
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Last Plumber said:
You would need to consult the manufacturers installation manual for that particular boiler.
I have seen all manner of configurations over the years but the manufacturer is the place to start if you're thinking of altering or installing something.

It was more out of curiosity as a newbie, @stedysons comment on pressure makes sense with the combi.

Aquarius · Aug 19, 2020

As per the others a consultation with the manufacturer would be a worth while chat. This is an extract from the Intergas (Netherlands based) eco rf30 manual which gives different configurations:

NewStart · Aug 19, 2020

steadyon said:
The following applies to the UK and its regulations:
1. You can have sealed systems with combi (always sealed), system boilers or open vent boilers provided the manufacturer allows this - these days they nearly all do.
2. You can't really run a combi boiler off an F&E tank, as the pressure is unlikely to be sufficient to pressurise the system. Also, you'd lose the benefit of mains pressure hot and cold.

Why does a combi boiler require pressure to operate yet a system boiler doesn't?

Is this a protection mechanism or is it designed to increase the boiling point of the heating medium?

Aquarius · Aug 19, 2020

NewStart said:
Why does a combi boiler require pressure to operate yet a system boiler doesn't?

System boilers do require pressure to operate, it’s heat only/open vent boilers that do not. A sealed system only gets rid of the feed and expansion cistern in the loft. It can be fed onto a gravity hot water system or an unvented cylinder.

Last Plumber · Aug 19, 2020

NewStart said:
It was more out of curiosity as a newbie, @stedysons comment on pressure makes sense with the combi.

Oh I see.
I have seen Combi Boilers on open vented systems many many moons ago (Heating side only). You don't see it now though.

SJB060685 · Aug 19, 2020

We used to have a customer on an open vented oil combi. As above it was only the heating side though, the hot and cold was still mains pressure.

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Can a conventional system boiler be a closed system?

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