why is my combi boiler system pressurised

[jimbo123]

Simple as it may sound I have scoured the web asking 'why is my system pressurised at all' and cannot find an answer
Hoping for your help, Jim

 

[Gasmk1]

simple answer without being pressurised, a pressurised system does away with the need for a tank in the loftsyatem fed with water.

 

[Dotty]

The boiler is also designed to work with a minimum pressure of, on average, 1 bar.

Anything below this usually causes the boiler to shut down.

An average property using an open vent system would only have roughly 0.5 bar.

 

[jimbo123]

Thanks but I still don't get it.

Just to confirm:
The header tank in the loft (in an older house domestic potable water system) feeds the water to the hot water cylinder and pipes, and to the cold water system pipes.
The combi boiler does away with that and the hot and cold systems are fed from the mains.

The second tank in the older systems provides room for expansion as the water on the central heating system expands.

So why do we need a pressurised central heating system considering a pump is used to circulate the water around the radiators?

Could it be to provide a balance of pressure across heat exchangers or something?

 

[Gasmk1]

no the pressurised boiler has its own expansion vessel within it, as water expands as it gets hot/hotter

 

[jimbo123]

no the pressurised boiler has its own expansion vessel within it, as water expands as it gets hot/hotter

Thanks for your reply. I realise that there is an expansion tank within the boiler but I can't get my head around why the central system has to be intentionally pressurised to run.

Perhaps another way of asking the question would be - 'why does my boiler shut down if there is no pressure in the central heating system'

 

[Gasmk1]

Because having pressure in guarantees that it is full with no pressure the boiler can't be certain there is water in so this stop it dry firing and damaging the boiler

 

[jimbo123]

Because having pressure in guarantees that it is full with no pressure the boiler can't be certain there is water in so this stop it dry firing and damaging the boiler

Thanks a lot GasMk1, that seems the most logical answer - boiler protection.
One simple answer that none of the 'big boys' put in their boiler operating write ups or troubleshooting charts.
Thanks again

 

[gmartine]

A sealed pressurised system also prevents oxygen ingress which reduces corrosion as well as improving efficiency.

Tbf there's no reason why manufacturers would need to explain why or how their systems work to the public.

 

[jimbo123]

A sealed pressurised system also prevents oxygen ingress which reduces corrosion as well as improving efficiency.

Tbf there's no reason why manufacturers would need to explain why or how their systems work to the public.

Thanks for that, but I disagree with manufacturers not needing to explain their systems. A simple bracketed sentence the same as Gasmk1 gave would cost nothing. Or maybe others are not as inquisitive as me??!!

Jim

 

[Rickster123]

Thanks for that, but I disagree with manufacturers not needing to explain their systems. A simple bracketed sentence the same as Gasmk1 gave would cost nothing. Or maybe others are not as inquisitive as me??!!

Jim

Nothing wrong with being inquisitive Jim. I've often asked myself seemingly pointless questions.
Why do superheroes wear their underpants outside their clothes?
And why is it that if you spill water down your top it leaves a dark mark when waters clear?!

 

[gmartine]

Thanks for that, but I disagree with manufacturers not needing to explain their systems. A simple bracketed sentence the same as Gasmk1 gave would cost nothing. Or maybe others are not as inquisitive as me??!!

Jim

On the contrary, a manufacturer's technical author would need to confirm with a systems engineer what, how and why for no good reason other than you're inquisitive and don't know what those that are qualified do and when those that are qualified need to know they contact a manufacturers technical support. No harm in asking though.

 

[Stoney Ground]

Thanks a lot GasMk1, that seems the most logical answer - boiler protection.
One simple answer that none of the 'big boys' put in their boiler operating write ups or troubleshooting charts.
Thanks again

Maybe that's because they expect only competent GSR engineers work on their boilers.

 

[jimbo123]

Maybe that's because they expect only competent GSR engineers work on their boilers.

Wahay, passed a craftsmans exam have you!

 

[PlumbBobBob]

Wahay, passed a craftsmans exam have you!

wind your neck in matey

 

[Dotty]

In fact, you've had more than enough information to satisfy your curiosity.

Thread closed.