Fitting an expansion vessel

[Panyards]

Can someone tell me what the pre charge pressure should be for an expansion vessel on a heating system. Do I need to take the static head into consideration?
I am converting my son's heating system from the original header tank system to a sealed system and I can't find any info on this subject.

 

[superdupergasman]

Usually about 1 bar.

Slightly less for a large system i.e 0.75

Or for a very small system 1.5 bar.

its all in the ltrs and the vessle size but I'd just go for 1 bar

 

[Panyards]

Thanks for that. I should perhaps have said that the house is a 3 storey one with the boiler in the basement so the static head must be over 25 feet. Does that make any difference?

 

[Agile]

Look at the FAQ on this site!

You dont make it clear if its three stories including the basement or not.

If a total of three then I would advice a precharge pressure of 1.2 Bar and a cold system pressure of 1.8 bar.

Tony

 

[superdupergasman]

Where is the pressure gauge sited?? as this will also effect
the system pressure.

1.8 bar is too high IF the pressure gauge is at the top of the system, you would be looking at 2.8 bar at the bottom.

 

[Agile]

Thats a good point! I was thinking that the EXV would have been at the boiler but of course we dont know!

If its on the top floor then precharge of 0.6 Bar and water pressure of 0.9 Bar.

What I also forgot to ask is "Are you certain the boiler can be safely used on a sealed system?"

If so, have you fitted a pressure relief valve ?

Its often forgotten but this work can be dangerous if not done correctly!

Tony

 

[Panyards]

Thanks both this is really helpful.
The house has 2 floors plus rooms in the roof space plus a basement.
The boiler is in the basement and there are radiators in the top floor rooms. The Vessel has got a PRV as part of the expansion vessel control kit and the gauge is on the PRV.
The boiler is relatively modern but what are the concerns re. safety in converting to a pressurised system?
I understand that the EXV should be positioned relatively close to the pump on the suction side so I plan to install it on the ground floor so the PRV can drain outside.

 

[AlanE]

The boiler is relatively modern but what are the concerns re. safety in converting to a pressurised system?

If you don't know then it MUST follow you are not competent!!

What make & model of boiler? The manufacturers have deemed certain, even modern, boilers UNSUITABLE for use on sealed systems.

Why do you think they ave done this - could it just be on the grounds of SAFETY??

 

[Panyards]

Thanks AlanE for those comments. Does asking a question indicate incompetence?
The boiler is an Ideal - Mexico Super 3 rated 20.5 - 23.4 Kw. Is it suitable?

 

[twgas]

I dont think your boiler is suitable for sealing without a proper kit for the boiler, thats in addition to the vessel and prv kit you've already got.

 

[Panyards]

What is the proper kit for the boiler? Are they readily available? What does it do?

 

[twgas]

the kit is actually a safety device so should only be fitted by a RGI. it could prevent the boiler going BANG!!!!

 

[Panyards]

Would that be a high temperature manual reset cut-out??

 

[twgas]

I decline to answer that in case you decide to get one that is not right and it f***s your boiler, and possibly house too.

 

[Panyards]

But a Corgi could fit it I presume?