Should i get the expansion vessel replaced with a bigger one

[donmaico]

My central heating engineer seems to think it may be necessary at some point in the future but thought the boiler would work fine for now after the service he carried out on it.
The situation is as follows our boiler which is a rebadged Intergas combi ( Atmos) was installed about 12 years ago and not long after that we had an extension built and two extra rads fitted . It worked fine for several years until the point we had to have the inbuilt expansion vessel replaced. Fast forward to this month, and we noticed the pressure gauge was showing zero, so we called him out for a service. After he finished he seemed confident the boiler would run for several more years as it was running on 98% efficiency( or thereabouts) but he did suggest that a larger expansion vessel might be desirable if the pressure dropped a couple more times within the following year.
He serviced the boiler this past Wednesday and already I have to re-pressurise it twice at a time of the year when the CH is off so I am now wondering whether to follow his advice ASAP and whether he can fit an external vessel from a third party manufacturer . Atmos no longer supply boilers but they do spare parts, only problem being they are not the most reliable( his words).Can anyone advise me please?

 

[Swwils]

It sounds like your boiler is having recurring pressure issues. While the boiler can still run efficiently, the need for frequent re-pressurising indicates a problem. That pressure has to be going somewhere.

However, considering the age of your boiler and the lack of reliable spare parts, you might also want to consider the long-term cost-effectiveness of upgrading to a new heating system.

Ultimately, it's best to discuss these options further with a different professional.

I would be very dubious of the 98% efficiency claims, that would entirely be dependent on the design and installation of the system. It is extremely unlikely that is the actual achieved value.

What flow temperature does this system run at and what controls it?

 

[donmaico]

It sounds like your boiler is having recurring pressure issues. While the boiler can still run efficiently, the need for frequent re-pressurising indicates a problem. That pressure has to be going somewhere.

However, considering the age of your boiler and the lack of reliable spare parts, you might also want to consider the long-term cost-effectiveness of upgrading to a new heating system.

Ultimately, it's best to discuss these options further with a different professional.

I would be very dubious of the 98% efficiency claims, that would entirely be dependent on the design and installation of the system. It is extremely unlikely that is the actual achieved value.

Thank you. it did make me wonder, especially as I live in a hard water area on the south coast

 

[Madrab]

The size of the EV would have nothing to do with the system losing pressure, unless it was identified that the system capacity exceeded the ability of the current EV to absorb the expansion. It's a simple case of it's either larger enough or it isn't, there isn't a case of, it won't all of a sudden be large enough within the next year.

If the system pressure is now exceeding 3 bar when fully hot and then the PRV is dumping the pressure then either the current EV isn't pre-charge properly or it isn't large enough and needs increased in size. If the pressure isn't exceeding the PRV release pressure then the system is losing pressure somewhere else.

 

[donmaico]

The size of the EV would have nothing to do with the system losing pressure, unless it was identified that the system capacity exceeded the ability of the current EV to absorb the expansion. It's a simple case of it's either larger enough or it isn't, there isn't a case of, it won't all of a sudden be large enough within the next year.

If the system pressure is now exceeding 3 bar when fully hot and then the PRV is dumping the pressure then either the current EV isn't pre-charge properly or it isn't large enough and needs increased in size. If the pressure isn't exceeding the PRV release pressure then the system is losing pressure somewhere else.

"that the system capacity exceeded the ability of the current EV to absorb the expansion" that is what he was suggesting

 

[DP]

"that the system capacity exceeded the ability of the current EV to absorb the expansion" that is what he was suggesting

If that was the case, issue would have arisen when the expansion vessel was fitted, not many moons later. I suspect inability to properly charge up the vessel may be more of a clue.

 

[Madrab]

"that the system capacity exceeded the ability of the current EV to absorb the expansion" that is what he was suggesting

When it was fitted, it should have been tested - the system brought up to temp and the pressure checked. it would have been apparent at that point if the current EV wasn't larger enough by the excessive pressure rise, not 'maybe in a years time'.

As suggested if the current EV can't stop the pressure from reaching the Pressure Release Valve lifting pressure then it either needs setup properly (correct pre-charge set correctly) or needs enlarged, there is no 'might be' as far as this is concerned.

 

[donmaico]

When it was fitted, it should have been tested - the system brought up to temp and the pressure checked. it would have been apparent at that point if the current EV wasn't larger enough by the excessive pressure rise, not 'maybe in a years time'.

As suggested if the current EV can't stop the pressure from reaching the Pressure Release Valve lifting pressure then it either needs setup properly (correct pre-charge set correctly) or needs enlarged, there is no 'might be' as far as this is concerned.

"When it was fitted, it should have been tested" It was fitted by another engineer before we had two extra rads fitted. He came back once more so maybe he should have checked the pressure then. Since then, he disappeared, and I had a hard time finding another who was familiar with these single heat exchanger boilers with only 4-5 moving parts. I eventually found one who has looked after it for about 8 years or so and in that time has replaced the EV once already, but not for a larger one. I'll ask him about re setting precharge correctly as an alternative ti replacing the EV

 

[Johntheo5]

If you are only using the combi just now for DHW then EV capacity will not be the problem as it only has to absorb the expansion for a very .max volume of say 5L of boiler primary Water expansion of ~ 100ml. You might run it on DHW after repressurizing to say 1.5 Bar and note the pressure. As noted above if the pressure rises to 3 bar then EV precharge pressure far too high, normal precharge is 1.0 bar and a filling pressure of 1.5 bar.

 

[SpecialK]

Tie a bag around the PRV outlet. If there is water in there when the pressure drops you may need to properly recharge the EV or replace it. If not then you have a leak somewhere.
To determine if its on the heating or boiler side you can isolate the heating loop under the boiler. If the pressure still drops then something in the boiler is at fault.

Also if its dropping when the CH is not even used then it is more than likely not an EV fault.

 

[Madrab]

"When it was fitted, it should have been tested" It was fitted by another engineer before we had two extra rads fitted. He came back once more so maybe he should have checked the pressure then. Since then, he disappeared, and I had a hard time finding another who was familiar with these single heat exchanger boilers with only 4-5 moving parts. I eventually found one who has looked after it for about 8 years or so and in that time has replaced the EV once already, but not for a larger one. I'll ask him about re setting precharge correctly as an alternative ti replacing the EV

Going by all the evidence, I don't think the EV size may be at issue here. At no time during this elongated exercise has anyone suggested that the EV is undersized. A new EV may have been needed over it's lifespan but if the system pressure is stable, i.e. it doesn't run up to >3 bar when the CH is on now then it's not the EV, size or pre-charge. If at some time the EV was compromised then the system could have over pressurised and the Pressure Relief Valve (PRV) would have opened.

As suggested there may be an issue with the PRV as they are notorious for not sealing back down again once they have opened (when the old EV failed), especially if they're older. That can be checked by placing a balloon/bag over the outlet pipe or see if it's dripping.