Expansion vessel problem and blocked overflow?

[Lusi83]

Urgent question ...what happens if your expansion vessel has gone and your overflow is blocked ...
Long story but have good reason to believe the expansion vessel was on its way out and now boiler currently running at 3.5 bar and (although dark, raining and overflow at second floor height) I can't see any water coming out of overflow...

I did clear the overflow out about 9 months ago ..and it was well blocked ... but haven't got a ladder here at moment to check it again...

Can the pressure go elsewhere? Will something explode? Do I need to find a ladder asap?

 

[45yearsagasman]

Are you referring to your pressure relief or your condensate drain?

 

[Lusi83]

Its a combi - not a condenser - Worchester bosch CDI 35 II
Was told by plumber that if expansion vessel has gone pressure would go up to above 3bar and water would start dripping out of this overflow pipe...

Anyway think I can see a drop of water on overflow now and pressure is just above 3 -so it looks like it is ok...at least it isn't still going up...

Out of interest what would happen?

 

[petertheplumber12]

You can use a radiator to work as an expansion vessel, and drop the pressure at the same time. drain 2/3 of the water out of a reasonable sized radiator that doesn't mind not producing a lot of heat, you can do this quite easily, if you put a shallow container under one of the rad valves, then turn OFF both rad valves and undo the nut that joins valve to radiator a LITTLE bit, it will start dripping, when it stops dripping open the bleed nipple on the rad and it will carry on dripping, you may have to empty the container a couple or three times, but when the rad is nearly but not completely empty, tighten the nut back up, close bleed nipple, then open valves back to where they were.
If you deliberately empty too much out of rad then you can bleed some of the air out and that will drop the pressure. once it is down to 3/4-1 bar you should be ok.

 

[petertheplumber12]

If there is 3 bar of pressure to go out I don't think the pipe blockage would stop anyway. Bleed a rad now to drop the pressure catch the water that comes out with a bowl, it will be a liter or 2.

 

[Lusi83]

Will bleed a radiator....haven't got any of the right spanners here at moment to use a rad as an expansion vessel
(they are with the ladders in a house we are renovating ...always bringing things backwards & forwards -but still find whatever tool I want is always in the wrong house when I need it )

And will get back onto the plumber tomorrow to arrange for a new expansion vessel...

 

[billybaggins]

You sure its not a faulty gauge? If the safety hasnt blown at 3 bar its at fault too and should also be replaced. The vessel can be recharged using a bike pump.

If vessel is done your cheapest option is to fit an external one as boiler manufacturers know hoe to charge for a replacement internal one.

And its not an overflow its the pressure releif valve pipe or blow off pipe if ya like. Either way its for safety so if its not working replace it, probably around 10 quid.

 

[billybaggins]

Oh and usually a fitting will blow first, Very hot water will be expelled, though being a sealed system only a few litres will come out before it airlocks.

Also depending on condition a rad or heat exchanger could give way. Either way if its a rental and a tenant is scalded you could end up in a court case. A kid was killed a couple of years ago when a tank in a roofspace had heated from cylinder pumping over and the kid died and if i remember correctly the landlord went down for manslaughter. Thats on the extreme though and an open vented system with alot more water on the domestic side

 

[45yearsagasman]

What a very reassuring post Billybaggins, and what a load of misinformation relating to the point in question.

 

[Lusi83]

No worries - thanks 45yearsagas man - I guess Billybaggins message is if the pressure hadn't started coming down to turn the boiler off ...
Pretty sure it is the expansion vessel....
Been losing pressure on and off for a while now ...I had it repaired within the last year - a leak on HW side - plumber checked it out for leaks on rads etc at the time and said that the expansion vessel was probably on its way out too...and to keep an eye on it...also he checked pressure relief valve pipe -could see it was blocked and was going to come back with a ladder but I said I'd do it (when the storm we were in the middle of had passed!) and found it completely blocked solid for a good 2 inches...
Only realised pressure at cold was zero last week when I heard it come on and not sound very happy (excuse is I'm asleep when it is cold - it comes on at 3am for when partner gets up!) and it is 1+bar when hot ...so I thought that was ok and then it wasn't too urgent but better get it fixed...(also sure worchester bosch me years ago it wouldn't operate at zero pressure -it would cut off to stop damage)
Only got round to phoning plumber today and got told I might have ruined my pump! And to refill urgently -(and also I think he thinks I am an idiot)- hence letting it cool down and refilling it and watching for water coming out of 'pressure relief valve pipe' ...(and not wanting to phone him to ask him if I should be panicking!)
The safety pressure for my boiler is 3 bar and it does operate at zero - so I guess gauge might be a bit out ....
And I am having an external expansion vessel...