Possible Expansion Vessel problem?

[shamilt1]

I have a 10 year old Worcester Bosch 24i RSF combi boiler. The radiators upstairs were only getting hot at the bottom six inches. I topped up the pressure to 1 1/4 bar, bled each radiator - topping the pressure back up as it dropped. Thats about as far as my plumbing experience goes! Since doing that I have noticed that once the heating has been on a couple of times the pressure drops back down to zero. I had a search on here and it sounds to me like the expansion vessel. Unlike some posts on here though, my pressure doesnt go up to 3 bar and cut out. If its topped up to 1 1/4 bar when cold, the boiler gets up to about 2 bar and runs fine - only dropping down to zero pressure when its turned off. I looked at the pipe outside the house it was dripping when the heating was on. My next step is going to be pressing the valve to see if water or air comes out- but in the mean time, does it sound from the details given like it needs a new expansion vessel, or just that it needs some air putting in it - or does it sound like something else? Thanks for any help.

 

[stevetheplumber]

if its not getting up to 3 bar its unlikly to be the preasure vessel you must be loosing water some where most likley thing is preasure relief valve this will show outside where the pipe discharges

 

[desrob]

if its not getting up to 3 bar its unlikly to be the preasure vessel you must be loosing water some where most likley thing is preasure relief valve this will show outside where the pipe discharges

prv is discharging try re-seating valve

 

[shamilt1]

Thanks for your quick responses. Would you say the steady drip from the pipe outside points to the pressure relief valve then- or would water be coming out of it faster than that?

 

[PlumbBobBob]

any discharge from the prv points to it being the problem and will be a good idea to get it looked at.

 

[shamilt1]

Baring in mind that I am a complete novice- is this easy to do? I gather the prv is the red knob with 3 BAR stamped on it? How do I reseat it?

 

[desrob]

Baring in mind that I am a complete novice- is this easy to do? I gather the prv is the red knob with 3 BAR stamped on it? How do I reseat it?

get some one qualified to do it correctly for you

 

[shamilt1]

any discharge from the prv points to it being the problem and will be a good idea to get it looked at.

There is no water leaking from the boiler itself- is this what you mean, or do you mean the pipe outside? I will try and sort it myself if I can- my plumber isnt answering his phone!!!

 

[PlumbBobBob]

i mean the pipe outside which is connected to the valve with the red knob. you cannot really do this yourself. post where you are and there may be someone on here near you.

 

[shamilt1]

I'm in Keighley , West Yorkshire if anyone can take a look. Too difficult for a novice then I take it? I'm pretty handy & can follow instructions- but saying that, I dont want to flood the house

 

[mikegas]

There is no water leaking from the boiler itself- is this what you mean, or do you mean the pipe outside? I will try and sort it myself if I can- my plumber isnt answering his phone!!!

use somebody elses then

 

[shamilt1]

use somebody elses then

Any recommendations for a good one near me?

 

[mikegas]

Any recommendations for a good one near me?

might be someone on here close enough for you, just hang on a bit

 

[shamilt1]

I am now thinking about replacing the pressure release valve as they only cost a tenner. Also whilst im there checking the pressure in the Expansion Vessel. I have the original installation manual which gives a detailed description on how to change this valve. Is it really not a job I should be tackling myself- or is it more tricky than it sounds?

 

[Bigvespa]

I live in Bradford.......PM me....

 

[MattWeth]

The pressure relief valve is a safety critical item - it should only be serviced or replaced by a qualified engineer.

 

[shamilt1]

Okay- after studying my boiler a bit closer, I have a bit more info and found that my original post wasn't entirely correct. After topping up the boiler to 1 1/4 Bar from cold, I put the heating on. The pressure gauge steadily rises to around 2 2/3 Bar. The pipe which runs from the boiler to the outside of the house expells a steady drip which gradually increases to a steady trickle as the pressure rises. After the boiler gets to 2 2/3 bar, the pressure starts to decrease and the gauge slowly starts going the other way. The boiler continues to run all this time. Does the symptoms still point to the PRV or the EV. I'm going to press in the valve on the EV to see if any water comes out and pump some air into it if needed. Could that sort it? If that doesn't work, thats the end of DIY plumbing & its time to call in a plumber!

 

[shamilt1]

I have now had a look at my Expansion Vessel. With the water pressure at 0 Bar I pressed in the valve and no water came out- hardly any air came out either. I got my bike pump and pumped it up to around .8 Bar. When I did this the gauge on the boiler went up too, to around 1 Bar. I then tried the heating and the pressure still went up to around 2 1/2 Bar, before creeping back down - the pipe outside of the house from the PRV was still dripping. When it had all cooled down I checked the air pressure in the EV and there was hardly any air in it again!? Does it sound like the PRV still? Please help guys

 

[heliotrope]

Certainly appears to be fault with pressure vessel.

Test at the valve, if water comes out then requires new vessel. If no water then could just require repressurising with a
bike or foot pump.

Test the pressure relief valve by bringing up to correct pressure with boiler cold and observe whether any water dripping
when boiler off.

If still leaking when cold then replace (don't mes about trying to repair)

 

[shamilt1]

Certainly appears to be fault with pressure vessel.

Test at the valve, if water comes out then requires new vessel. If no water then could just require repressurising with a
bike or foot pump.


Test the pressure relief valve by bringing up to correct pressure with boiler cold and observe whether any water dripping
when boiler off.

If still leaking when cold then replace (don't mes about trying to repair)

Thanks for your reply. As stated in my post, the was no water coming out of the vessel and I repressurised it. When the boiler is at correct pressure when off and cold, there is no water dripping. Water only drips when its up and running.

 

[Simon F]

the charge pressure in the expansion vessel should be 0.7 bar, the manufacturer may specify different. this needs testing without the pressure in the system affecting it, ie boiler flow and returns closed and drained. you really should get someone registered to test this for you.

 

[heliotrope]

Ok, 0.8 is not exessive for this boiler, just be sure that system completly depressurised before
pumping up. (0.5 to 0.6 the optimum).

No isolators turned off etc.


Although no water coming from valve it could still be split bladder in vessel.

This would need replacing or (easier) a new vessel fitted remote from boiler.

 

[shamilt1]

Okay, got my pressure vessel sorted- held open the PRV ( as its leaking anyway) and pumped up to the correct pressure. This has sorted out the pressure problem and it now only rises to just below 2 BAR with all the radiators boiling hot . Im going to have a go at fitting a new PRV. Does this procedure sound okay- bleed the radiators so there's no air in the system, screw down auto air vent, drain boiler with the PRV, fit new PRV, then re- pressurise to 1 1/4 BAR? Thanks.