Heat only boilers and confusion

[kasser]

Trying to get to grips with all the terminology here and what can be done with what.
Heat only = open vent boiler?

I suppose nothing stops me from sealing it up and sticking an expansion vessel to it? This is the same as a system boiler then? Is it cheaper then to buy a system boiler instead of adding an expansion vessel to the heat only? Even with a system boiler you may need an extra EV anyway, so what's the advantage of picking a system boiler in the first case if you're going to add an EV to it?

Is there anything stopping me from having an open vent heating system and an unvented hot water cylinder with a heat only boiler? Or vice versa?
There's no reason I can't have an open-vent hot water cylinder with a system boiler?

If I'm right in my above thinking, a heat only boiler can be used as a system boiler with the right components, but a system boiler cannot be used as open-vent boiler due to the expansion vessel? I suppose you could, by ignoring the EV, but then you're paying more for nothing?

This is confusing me more:
https://www.vaillant.co.uk/for-installers/products/ecofit-pure-open-vent-boiler-26116.html
If you look under Specifications and DHW, it mentions a minimum pressure to operate the boiler. Why, what for?


Finally, with a cold water tank in the loft and bathroom just below, the tank is going to be less than 1 m above the shower head when taking a shower. That's 0.1 bar of pressure minus losses due to pipe length and fittings. Not possible to have a shower then? I suppose this was designed to fill a bath, so large pipes, big flow rate, low pressure?

 

[gmartine]

I'll let the others answer the rest as this was a curiosity to me and I have to pop out.

"This is confusing me more:
ecoFIT pure | Open Vent Boiler | Vaillant UK
If you look under Specifications and DHW, it mentions a minimum pressure to operate the boiler. Why, what for?"

Safety, stop it running dry.

 

[ShaunCorbs]

Heat only can be used for either open or sealed if manufacturers approve

System boiler includes expansion vessel, pump , blow off etc normally sealed

 

[EvilDrPorkChop]

The way I look at it is that on a system boiler the pump, EV, Auto Airvent and blow off are all covered under the manufactures warranty with the boiler, for however long that maybe (Usually 7+). System boilers are usually only price of a pump more (That you would usually replace on when fitting a heat only boiler anyway) so it makes more logical and cost effective sense to have a system boiler over a heat only one in most cases.

Depends on the situation, space and installation. If theres already a EV and pump in then it makes more sense to fit a heat only.

 

[Rob Foster]

Trying to get to grips with all the terminology here and what can be done with what.
Heat only = open vent boiler?

I suppose nothing stops me from sealing it up and sticking an expansion vessel to it? This is the same as a system boiler then? Is it cheaper then to buy a system boiler instead of adding an expansion vessel to the heat only? Even with a system boiler you may need an extra EV anyway, so what's the advantage of picking a system boiler in the first case if you're going to add an EV to it?

Is there anything stopping me from having an open vent heating system and an unvented hot water cylinder with a heat only boiler? Or vice versa?
There's no reason I can't have an open-vent hot water cylinder with a system boiler?

If I'm right in my above thinking, a heat only boiler can be used as a system boiler with the right components, but a system boiler cannot be used as open-vent boiler due to the expansion vessel? I suppose you could, by ignoring the EV, but then you're paying more for nothing?

This is confusing me more:
https://www.vaillant.co.uk/for-installers/products/ecofit-pure-open-vent-boiler-26116.html
If you look under Specifications and DHW, it mentions a minimum pressure to operate the boiler. Why, what for?


Finally, with a cold water tank in the loft and bathroom just below, the tank is going to be less than 1 m above the shower head when taking a shower. That's 0.1 bar of pressure minus losses due to pipe length and fittings. Not possible to have a shower then? I suppose this was designed to fill a bath, so large pipes, big flow rate, low pressure?

Quite a number of the questions you ask you have quite obviously got the general answer to already. Small houses and flats are ok for combi set ups, larger homes with more than one bog, showers etc ..no way. Then you enter system boiler land a pressurised conventional type system with out high level intermediate water storage tanks etc. but still dependant on the mains water supply ...not just pressure but volume..check your supply
then report back here with your
figures and we will advise

centralheatking

 

[Aire]

Quite a number of the questions you ask you have quite obviously got the general answer to already. Small houses and flats are ok for combi set ups, larger homes with more than one bog, showers etc ..no way. Then you enter system boiler land a pressurised conventional type system with out high level intermediate water storage tanks etc. but still dependant on the mains water supply ...not just pressure but volume..check your supply
then report back here with your
figures and we will advise

centralheatking

What's a bog got to do with whether a combi is suitable or not?

 

[Rob Foster]

What's a bog got to do with whether a combi is suitable or not?

If you have plenty of bathrooms
..bogs ...then everytime some one goes for a dump this will
mess up,the flow to the shower
etc. chking

 

[Aire]

If you have plenty of bathrooms
..bogs ...then everytime some one goes for a dump this will
mess up,the flow to the shower
etc. chking

Well the amount of toilets a house has wouldnt influence my decision on a combis suitability. Baths, showers and flow rates are all that matters in my opinion.

 

[kasser]

Safety, stop it running dry.

But there's no DHW in heat only boilers, and especially no pressure in this context? It's just the hot water for heating running through the hot water cylinder instead of a rad... Whatever pressure you have in your rads will be the same running through the cylinder?

 

[kasser]

In what way is a system boiler dependant on mains pressure? If you fit a vented cylinder, no problem? May only be an issue if mains pressure is < 1bar; you can't pressurise your heating system then?

 

[Rob Foster]

In what way is a system boiler dependant on mains pressure? If you fit a vented cylinder, no problem? May only be an issue if mains pressure is < 1bar; you can't pressurise your heating system then?

So if there is a shortage of incoming mains water ...where does it come from really
chking

 

[Riley]

This is such a weird thread

 

[Rob Foster]

Well the amount of toilets a house has wouldnt influence my decision on a combis suitability. Baths, showers and flow rates are all that matters in my opinion.

of course it does it affects the total demand for the property
esp at peak times when kids come back from school or in the morning when everybody is bathing or showering...intermediate high level,storage was the nirmal forva very good reason ...off to
Bristol have a good rest of day
chking

 

[kasser]

So if there is a shortage of incoming mains water ...where does it come from really
chking

This problem would apply to all 3 types of boilers.

 

[Last Plumber]

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