Pressure for sealed heating system...

[brooky_agb]

Hi,

I'm going to attempt to drain and refill my heating later. I watch a really good YouTube video about how to do it and I'm confident I can do this easily.

What pressure should I refill too on my sealed system. The video said 1 Bar but we have had issues circulating heat around before as our house is a plumbing hotchpotch of 21 radiators. Does it have to be 1 Bar or can I take it higher than that?

 

[lifesagasman]

1 bar will make it work fine.

21 rads??

 

[brooky_agb]

Approx 21 rads yeh. The boiler is a chunky mother...

http://www.worcester-bosch.co.uk/homeowner/products/oil-boilers/greenstar-heatslave-external-2532

The plumber was supposed to powerflush it and its been in almost three weeks now with Fernox F5 in!! I've decided to damned well do it myself as he never turns up.

 

[lifesagasman]

straightforward job then. bon courage! and you'll save sheds of wonga..

 

[brooky_agb]

Well the plumber has been paid already so I'm doing his work for him. Actually trust myself to do it ok. I've done this before with a vented heating system (the old one). Wish me luck.

 

[MANDATE]

It could be higher than 1 bar, but not by much.
The system will be designed so the rise in pressure due to the expansion of water when its heated will be about 1 bar. So you have 1 bar rising to 2 bar, or 1.5 bar rising to 2.5 bar.
Two things you must be aware of.
First the pressure relief valve will open when pressure reaches 3 bar, so going from say 1.8 bar rising to 2.8 bar is inviting problems.
Secondly! this rise of 1 bar is based on the expansion vessel having all air and no water within it when it was first pre charged and installed. This will accomadate the excess water as the air gets compressed.
Over time the vessel may lose some of it pressure, which means the vessel may then already hold water before expansion takes place.
If this occurs, it means there is less air to compress which results in a large rise in pressure, followed by the PRV opening, followed by a drop in pressure, followed by the need to top up the pressure again and start the whole process over again.
If you're draining your system this will be the ideal time to check the air pressure in the expansion vessel, knowing there is no water within the vessel.

 

[brooky_agb]

Thanks Mandate. So I have to keep my eyes on it for a few days to make sure the cold pressure always sits at 1 bar and no lower as it may lose pressure as air is lost with bleeds.

 

[lifesagasman]

the gauge reading will fluctuate a little between hot and cold system temp.

bon courage means good luck. in foreign

 

[brooky_agb]

Merci Bien Monsieur! Do you have to be French to do this too?

I'll make sure I swear in French if things start going wrong.

 

[lifesagasman]

franglais

 

[MANDATE]

It will lose some pressure when you bleed a radiator, so always adjust after bleeding
Also some boilers have pressure switches so they won't start if pressure is too low.
Keep a watch on the rise in pressure, ideally 1 bar. If you find it around 2 bar rise that will be a sign of expansion vessel problem.
Be prepared with 'foot pump' and 'air pressure gauge'

 

[brooky_agb]

It's a spanking new boiler so it should all be ok.

It replaced a 25 year old predecessor.. that actually seemed to work ok. It just wasn't very efficient!! How times have changed...

 

[lifesagasman]

new doesn't always mean good

 

[brooky_agb]

Hope so its a decent brand.

 

[lifesagasman]

why are you flushing the system after fitting a new boiler? that should be done first to avoid all the crap blocking up the new one.