Expansion vessel worcester 28i

ginsterpies · 22 Feb 2010

Hi,
New to the forum. I've recently moved into a house with a 28i junior, and have had nothing but problems with the pressure. Shortly after we moved in, it kept cutting out due to overpressure. I had the british gas man came out and he repressurised the expansion vessel with a foot pump. That was a few months ago, and I now have the same problem. The pressure is below 0.5 bar when cold, but then goes up to over 2.5 when operating. I don't want to call gas man out again if I can help it, but not too sure on where the valve is for pumping up the expansion tank, and the proper procedure for doing so. Can anyone advise?

cheers,

Andy

selmar47 · 22 Feb 2010

I have a Worcester 28 cdi rsf combi boiler and the pressure vessel schrader valve is on the bottom left hand side of the vessel as you are facing the boiler. I am no expert regarding how to pressurise the vessel, but it does tell you how to do it in the owners' manual, or at least it does in mine. Basically you use a car tyre type pencil pressure gauge to see what the pressure is and then using a foot pump or bicycle pump with an adaptor for car tyres, you pump the pressure to around 0.5 to 0.7 bar. These figures equate approx to 7 and a half psi to 10 psi. I had a similar problem with high pressure on the boiler that was down to an internal leak inside the water to water exchanger and after replacing this all was back to normal. You usually get water coming out of the overflow pipe which is normally found outside coming out of your exterior wall somewhere. Once the pressure has reduced through the blow off valve the water will cease to appear from the overflow. The reason high pressure increases through the water to water exchanger is because mains water is going into your central heating system which once pressurised to around 1 bar is supposed to be separate from your hot water circuit and is a closed circuit. I hope I haven't confused you too much and this may not be your problem, but sounds very similar to the one I had. Good luck!

ManxPlumber · 22 Feb 2010

You need to neutralise system pressure first!

MANDATE · 22 Feb 2010

You'll find the procedure near the top of the plumbing & central heating page. ie 'Sticky' FAQs.
Basically when water is heated, it expands. The expansion vessel is designed to take this excess water. There needs to be virtually no water in the vessel, which leaves a good quantity of 'air' that can be compressed without too much rise in pressure. ie 1 bar
If there is not much air in the vessel the pressure will rise very high at a faster than normal rate, until the PRV opens when pressure will be lost.

The air valve may leak a little over time and lose some of the initial pre charge pressure. The problem when re-charging a vessel which has excess water in it, is making sure the excess water has been forced out of the vessel. Just increasing the pressure to 0.8 bar will not solve the problem unless the excess water has also been forced out of the system, which requires an open vent for this to happen.

hammerswinger · 23 Feb 2010

Check that the small pipe that connects to the Expansion Vessel (EV) isn't blocked as this will give the same symptoms as the EV having lost its air or it being knackered.

Agile · 23 Feb 2010

The communication pipe to the EXV is checked when the proper procedure for repressurising the EXV.

Tony

Agile · 23 Feb 2010

Agile said:
The communication pipe to the EXV is checked when the proper procedure for repressurising the EXV is used.

Tony

hammerswinger · 23 Feb 2010

Agile said:
The communication pipe to the EXV is checked when the proper procedure for repressurising the EXV.

Tony

Good point...Noted

Agile · 23 Feb 2010

But ONLY if the correct procedure is used.

Oddly BG dont seem to teach how to use the correct procedure.

I have seen two installations where they just added some air without depressurising.

Worse still another two installations where they had fitted seperate EXVs and left them pressurised as supplied at over the operating pressure.

However, those two mistakes on their part gave us £168 of work so some would say dont complain.

Tony

ginsterpies · 26 Feb 2010

thanks everyone - got everything done last night, and the boiler seems to be running with much more normal pressures now... 1bar when cold to 1.5 when hot.

cheers,

Andy

ollski · 26 Feb 2010

Agile said:
But ONLY if the correct procedure is used.

Oddly BG dont seem to teach how to use the correct procedure.

I have seen two installations where they just added some air without depressurising.

Worse still another two installations where they had fitted seperate EXVs and left them pressurised as supplied at over the operating pressure.

However, those two mistakes on their part gave us £168 of work so some would say dont complain.

Tony

The first one doesn't surprise me but I can't think of any expansion vessel for a domestic system that is pre pressurized at over 1.5bar which is a perfectly fine pressure to run at.

Agile · 26 Feb 2010

Both were stand alone EXVs and were at 2 Bar.

One even had a lablel still attached giving the precharge pressure and saying it needed to be reduced to suite the application.

Normal charge pressure should be about 0.7 or the set pressure on a heating system but equal on an unvented.

Tony

ollski · 26 Feb 2010

I'm not sure which they would be then, bg only have two externals on the laptop and I've used both. I think the 12l is set to 1.5 bar but I leave it at that and set the system pressure the same....never ever had an issue.

Agile · 27 Feb 2010

One was about 12 li. It had been added because they thought the boiler EXV was failed on a Puma. In fact it was OK but the communication pipe was blocked!

The other was 50 li but the owner thought that BG had pumped it up.

Tony

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Expansion vessel worcester 28i

Similar threads