Combi pressure through the roof!

[mikedelderfield]

Hi there.

Back again.

I have a combi boiler, sealed system.

I have taken one of the rads out of the system to do some decorating. Closed off the valves, removed the rad etc.

The cold pressure on the boiler was at 1.2 bar. I turned the central heating on and the pressure went through the roof. Expansion tank overflowed etc, all very wet.

Why did this happen?

Do I need to work quickly and get the radiator back on before we become hypothermic?

Any suggestions greatly appreciated.

Thanks

Mike D

 

[breezer]

its only a guess, was the rad you removed far from the boiler, i figure it is, so the boiler had the same amount of pressure, but a shorter distance for it to go so less room to expand so presure goes up and off goes your prv.

But then again i could be wrong

 

[mikedelderfield]

The rad was an upstairs one.

I think there are two rads between it and the boiler. When I took the rad off the pressure on the boiler dropped to about 0.4bar. There was a bit of leakage out of the valves overnight, which I assumed accounted for the pressure drop.

I filled the pressure upto 1 bar then fired up the boiler. Thats when the pressure really took off.

So should I drain/bleed the system a smidge to reduce the pressure to c0.5bar then try again?

Mike

 

[30kw]

Sounds like expansion tank not pressurised with air or the diaphragm gone. Drain the entire system and check expansion charge with a foot pump, it should be at 1 bar, if not pump up to 0.5-1bar, refill system pressure to 1 bar. If any signs of water at schredder valve then suspect a new expansion.

Alternatively u may have an airlock, does the boiler overheat and shut off gas?

 

[oilman]

No need to drain the entire system. Look up lots of recent posts on checking expansion vessels.

I don't understand why your

Expansion tank overflowed etc, all very wet.

How did it overflow? Has it burst? Is it an expansion tank or an expansion vessel?

The pressure should be set in the vessel with zero system pressure. Use the pressure release valve, that's what it's for. The air pressure you need for the topmost radiator being 16 feet above the lowest system point is 0.5bar. So if you have a two storey dwelling 0.5 bar is enough. Any more adds unnecessary stress to the diaphram when the water expands.

 

[mikedelderfield]

Not sure if it's an expansion tank or vessel. The boiler is a Ravenheat RSF820/20.

We moved into the house fairly recently and there is no User Manual to be seen. I have ordered a manual from Ravenheat, which should arrive any minute.

The boiler is located in the kitchen above some worktops. When the water pressure gets somewhere above 3 bar. Water drips out of a drain pipe onto the worktops (presumably from the expansion vessel).

I think the system we have is either quite old or just generally badly installed. Too many radiatiors linked on 15mm pipes etc.

So if I understand correctly; I should release on water pressure within the system using the pressure relief valve? Then set the pressure within the expansion vessel at 0.5 bar? Do I need a separate pressure gauge to read the expansion vessel pressure?

Perhaps things will be clearer when the User Manual arrives

 

[oilman]

You should release the pressure, then check to see if there is water in the expansion vessel before doing the setting up exercises. You should also disconnect your filling loop because, 1)it is illegal to leave it connected, and 2) the valve from the mains may be letting by which could destroy the expansion vessel in a spectacular way.

The discharge pipe should be routed outside not over the worktop. I think you should call an engineer in as it's been nearly a week since your first post. I reckon to fix things within a day when someone tells me they have sealed system problems.

 

[mikedelderfield]

I've not really looked at the boiler since my last post.

When I took the radiators off most off the plaster came off the walls with them. So I have been concentrating on replastering.

I am awaiting the Ravenheat User Manual before I do anything else. I will probably fit the new rads, have a look at the expansion vessel, see what other checks I can do myself. If everything looks OK, refill the system, give it a try, keep an eye on the hot water pressure. If it does not look good I will get an Engineer in.

The filling loop is attached, which I will disconnect. It does not seem to be letting water past, as the cold water pressure is stable.

Thanks

Mike D