To fill expansion vessel with water?

[Mouton]

Hello! I’m wondering which will cost more - to run our heating system with an inefficient/broken expansion vessel for a minimum of six months from now, or to call out an engineer (£100 excess). Our house is a new build and still under warranty. I noticed the pressure in our unvented system dropped to zero within a day of being topped up. No obvious leaks, so it’s likely there is a hole in the expansion vessel membrane.
The plumber won’t come out to meet the terms of the warranty except in emergencies during the restrictions. He has suggested we just keep refilling the loop until the vessel is filled with water (which will seep through the hole in the membrane). This sounds to me like it will add up to a lot of fuel inefficiency over the next 6-18 months or however long the restrictions last. Sooo... would it be more cost effective to call another company out to replace it (ie not under the warranty) and instead pay the £100 cover excess? We have a cancer victim living here, so they ought to at least do that. Our gas bill is normally about £350 per year, if that helps with calcs.
[automerge]1585653779[/automerge]
Should add that’s about 6350kWh of gas per year when the system is working as it should.

 

[ShaunCorbs]

If it is the expansion vessel it won’t hold that much water so would be full within a fill up so I don’t think the expansion vessel is a fault if you’ve topped the system up more than twice / three times

 

[John.g]

Top up to 1.5 bar (cold) and watch pressure rise when system heats up, if it doesn't rise above 2/2.5 bar and subsequently falls to 0 bar then you have a leak somewhere, if, after top up and system heat up, it rises to 3 bar and subsequently again falls to 0 bar when cold then the expansion vessel (diaphragm) is either holed or the pre charge pressure is either too high or too low, in all three cases the boiler PRV should lift and you should see this outside the boiler. Topping up every day will have little or no effect on the boiler efficiency/running costs but will eventually lead to system corrosion. If it is rising to 3 bar when hot, I can suggest a temporary solution by utilising a infrequently used radiator.

 

[SJB060685]

If you have a faulty expansion vessel or leak then you're losing heated water, which in turn requires more fuel to achieve desired temperatures.
You have a cancer sufferer so this needs to be sorted.
Is the expansion vessel external to boiler? Does it have a flexi to it kinked or possibly blocked?
As John says above a radiator can be used as a makeshift vessel.

 

[Mouton]

Wow! Thank you, so many replies

I've never noticed the pressure change while heating is on, even before the pressure started dropping rapidly post-top-up. It has always remained the same, regardless of temperature, until it developed this problem. I had noticed that I was having to top it up more and more frequently over the months and years.

I've looked all over for a potential leak, but can find no evidence of one... yet! That said, I wouldn't put faulty pipework past the plumbers who worked on this estate...

The vessel lives in the airing cupboard with the cylinder (upstairs). The boiler is downstairs. The PRV is very helpfully located on the other side of the house from any exit and on the neighbour's drive, which makes it difficult to monitor, but tomorrow morning I'll hang around his big new car and watch it.

British gas have stepped in to help us out- not for free, of course - but it will mean one less thing to worry about if they can fix it. If not, I might need to take you up on that radiator trick...

Yes, cancer person requires looking after! Thankfully they're in relatively good shape these days, but I don't really want to undo that by subjecting them to low temperatures.

Once the engineer has diagnosed the heating issue, I will come back and update this thread for future users

 

[SJB060685]

Put a balloon with rubber band over it etc to see if you catch water

 

[Mouton]

Update: engineer confirmed the expansion vessel is indeed rather broken. As for viral protocol, we had all sorts of fun cleaning down door handles etc., and with locking ourselves in one room while he suited up and worked in the rest of the house.

Anyway, the vessel is already completely full of water, and that means some parts need to be replaced and continually topping up isn't going to be the way to handle it for the next however many months. As you suggested, the PRV was expelling water to cope with the faulty system. Thankfully the new parts will come on Monday and we should be all good from then.

Amazingly, the developer are now claiming that because we have employed an engineer other than theirs (who refused to come out), we have invalidated the warranty. So I consulted a solicitor. Nowhere is it written in their warranty that we cannot employ someone else to service or repair boiler/cylinder/plumbing. Incredible that they dare to pull this nonsense in the current situation.

 

[EvilDrPorkChop]

Update: engineer confirmed the expansion vessel is indeed rather broken. As for viral protocol, we had all sorts of fun cleaning down door handles etc., and with locking ourselves in one room while he suited up and worked in the rest of the house.

Anyway, the vessel is already completely full of water, and that means some parts need to be replaced and continually topping up isn't going to be the way to handle it for the next however many months. As you suggested, the PRV was expelling water to cope with the faulty system. Thankfully the new parts will come on Monday and we should be all good from then.

Amazingly, the developer are now claiming that because we have employed an engineer other than theirs (who refused to come out), we have invalidated the warranty. So I consulted a solicitor. Nowhere is it written in their warranty that we cannot employ someone else to service or repair boiler/cylinder/plumbing. Incredible that they dare to pull this nonsense in the current situation.

Out of interest how old is the system?

 

[Mouton]

Out of interest how old is the system?

It’s 4.7 years. Warranty is 5 years.

 

[EvilDrPorkChop]

It’s 4.7 years. Warranty is 5 years.

Has it been boiler and system been serviced every year and the expansion vessel checked on the service? To be fair these should be regularly checked on a service - if it hasn't then I'm afraid it wouldn't be covered under the builders warranty.

 

[John.g]

It begs the question, how is a expansion vessel checked? is the system drained down and the pre charge pressure checked/adjusted or in the case of a gas boiler; is it isolated and drained to check? Some would hold that all EVs should have a isolation valve to facilitate drain down without draining down the system, some say that this shouldn't be allowed as the EV is considered as a safety device but IMO it isn't as the diaphragm can and does rupture without any warning, the safety device is the PRV.
I believe that even some oil boiler manufacturers will not honour their warranty if the EV is proven to be undersized in the event of a boiler leak which is a bit strange to say the least, On any pressure vessel, the PRV should be set to the safe working pressure of that vessel.

 

[Mouton]

Yes, I’m well aware of that. It passed the last inspection. Everything was serviced on a regular basis.