Intergas expansion vessel change issues

[snes]

Okay, I feel a bit of a plum here (not unusual) - my son's Intergas HSE 36/30 Compact boiler had the expansion vessel fail. After contacting Intergas for a quote (£490) he gave the job to me.

As the expansion vessel is behind the boiler, replacing it would have been a boiler off the wall job - therefore Gas Safe only - so I went down the route often recommended on here, an external expansion vessel.

I chose a 12L vessel as it seemed a more suitable size for the property than the 8L fitted. It was primed to 0.9 bar as per Intergas recommendation (I phoned them!) and was connected to the Tesla(?) fitting below the boiler where the original had been connected.

The PRV valve was also replaced as it had been letting by with the failure of the old vessel.

All this was achieved without removing the room sealed casing, so hopefully I won't have Agile chasing me up!

Having refilled the boiler and bled via the top valve, all seems to be working on the boiler except that the pressure, at 2.7 bar is higher than when I set it at 0.8 and the PRV valve is letting by again.

Have I overlooked something obvious here? For example, should I have tried to bleed the new expansion vessel even though it has no valve or would the water find its way in there automatically?

As far as the boiler is concerned, nothing has changed except that it has a new, larger, expansion vessel outside instead of inside and connected at the same place as the original.

Thanks for your patience in reading this far...... any ideas?

 

[Johntheo5]

the primed or precharging pressure was 0.9bar, what pressure did you charge/fill it to, normally 1.3 to 1.5bar cold, is the filling line disconnected?

 

[Madrab]

Are you talking about this connection?

How did you connect it onto that valve - if I remember rightly it's a 3/8" connection? If it's still over pressurising and the pre-charge is set properly then I would suggest that there is an issue with the connection from the EV to the system at that point, normally with an external then it would just be a connection @ the filling loop and use the EV coupler as the new loop point.

 

[snes]

John, the EV was pre-charged to 0.9bar and the cold fill was then filled to the same pressure. These pressures were as per Intergas recommendations.

Madrab - the existing 3/8 connector was removed from the valve and replaced with a brand new EV coupler at the same point. The EV coupler was an official Intergas part for this boiler.

One issue that might be worth mentioning - the drain off point at this valve does not seem to work. Loosening the blue plastic knob releases a mere trickle of water. As this drain off is right alongside the EV take off point, could there be some kind of blockage here?

Thanks for both your replies!

 

[Johntheo5]

John, the EV was pre-charged to 0.9bar and the cold fill was then filled to the same pressure. These pressures were as per Intergas recommendations.

Madrab - the existing 3/8 connector was removed from the valve and replaced with a brand new EV coupler at the same point. The EV coupler was an official Intergas part for this boiler.

One issue that might be worth mentioning - the drain off point at this valve does not seem to work. Loosening the blue plastic knob releases a mere trickle of water. As this drain off is right alongside the EV take off point, could there be some kind of blockage here?

Thanks for both your replies!

Is the cold fill disconnected or is it one of those permanently connected contraptions from the cold mains at the combi ( if a combi?) to the boiler flow or return, is so, this might be passing?.

One other thought is the possibility of the DHW heat exchanger failing and the system being over pressurized from the cold mains? although I think Intergas claim that they never fail.

What is the PRV setting?,

Its a very poor practice IMO not to fill the EV to say 1.3/1.5bar as this gives a nice little reserve of ~ 2.9L when cold without having to continually top up or worse having one of those infernal auoto top ups (just a PRV permanently open) which nicely mask any leaks.
Your 12L EV with precharge & filling pressures of 0.9/1.5bar will still only rise to 2.04bar when hot with a system vol of 100L. or only 1.75bar if filled to 1.3bar with still a nice reserve of 2.1L.

 

[Madrab]

One issue that might be worth mentioning - the drain off point at this valve does not seem to work. Loosening the blue plastic knob releases a mere trickle of water

There may be a problem with that valve then. If the drain off is blocked then the tapping to the EV outlet may be blocked too.

If that's the case then you may not even have an issue with the original Expansion Vessel (EV) - how was the original EV tested before the decision was made to replace it or was that just because of the high pressure? Was the vessel itself tested?

 

[Johntheo5]

If it is blocked then the pressure at the EV air end will still only be 0.9bar so worth checking?.

 

[snes]

John - the EV was pre-charged with nitrogen to 1.5 bar from new. I reduced that to 0.9bar as per Intergas advice. Am I allowed to recharge this (using air via a bike pump) back to 1.5 bar (or higher) as you say this will provide a greater operating margin? Your advice and experience here are much appreciated!

Madrab - the EV released significant water when the Schrader valve was depressed, so had definitely failed. When the coupling was disconnected and positioned over a bucket, pumping air into the Schrader valve to clear the vessel of remaining water (I hope I have explained this well) released a lot of brown and black dirty water indicating perhaps that the EV had decomposed a bit inside. Perhaps some of this crud had caused the blockage in the isolating valve? I have ordered a new valve in case the existing one is unserviceable. Again, thanks for sharing your expertise!

 

[Johntheo5]

John - the EV was pre-charged with nitrogen to 1.5 bar from new. I reduced that to 0.9bar as per Intergas advice. Am I allowed to recharge this (using air via a bike pump) back to 1.5 bar (or higher) as you say this will provide a greater operating margin? Your advice and experience here are much appreciated!

NO, you must depressurize the EV at the water end, you then check/pump the air end, a bike pump is fine, to 0.9bar only, you then charge/pressurize the water end to1.5bar, so 0.9 precharge (air end) pressure and a charging pressure of 1.5bar.

Have you checked the charging/filling arrangement, a photo would be nice.

 

[snes]

Ah, thanks! I got it the wrong way round.

Not on site atm, so can't post a photo. The filling loop, going from memory, is permanently connected, going from cold potable to boiler flow. Having removed and replaced the prv without any water issues, I'm guessing the filling loop is not passing when closed.

Thanks again for clarifying!

 

[snes]

John - apologies - missed your reply re checking the EV air side pressure. Hadn't thought of that!

Will do so when back on site.