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Can a conventional system boiler be a closed system?

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?
 
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

Esteemed
Plumber
Gas Engineer
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.
 
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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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

Plumber
Gas Engineer
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:
 

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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

Plumber
Gas Engineer
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.
 
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.
 

Alan Wright

Official Sponsor
I come across people who have been persuaded to replace their vented systems with a combi boiler only to find that the incoming water supply is poor. The boiler drops out due to low pressure when they turn on a shower and boosting the incoming water supply is only good for the one shower with a SPB. If they want what they had before in terms of running multiple taps and showers and in particular baths then they need to go back to a vented system.

I believe that using the new combi as part of a reinstated vented system would work other than when someone turns on a tap when the combi is heating the hot water tank (in which case the combi would temporarily switch off).

Is my logic sound?
 
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