I own a ground floor flat in a converted Victorian house in Nottingham. The building has three flats sharing a communal gas boiler (Vaillant ecoTEC plus 838, installed around 2017) which feeds a pressurised hot water system serving all three units. Over the past six weeks the system has been losing pressure at a rate of about 0.3 bar per week, requiring someone to top it up via the filling loop every few days.
I have checked the obvious things. No visible leaks on any of the accessible pipework in my flat or in the communal hallway where the boiler is mounted. The pressure relief valve discharge pipe outside is dry. The radiators in all three flats have been bled recently with no significant air coming out.
My working theory is that the expansion vessel has lost its nitrogen charge. On an ecoTEC plus 838 the expansion vessel is external (mounted on the wall next to the boiler) and the typical charge pressure should be around 0.75 bar when the system is cold and depressurised. I have not tested this yet because I am not sure whether I should be touching communal equipment unilaterally.
The questions are:
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Is recharging or replacing the expansion vessel something that falls under general maintenance (i.e. a service charge item) or would it require freeholder consent given it involves the communal boiler?
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Has anyone dealt with a similar situation in a converted property where the lease is unclear about who is responsible for the boiler? Our lease says each leaseholder contributes one third to “heating plant and associated equipment” but does not define what counts as maintenance versus improvement.
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If the expansion vessel does need replacing, am I right in thinking any Gas Safe registered engineer can do this, or does it need to be the original installer?
The boiler itself was last serviced in October 2025 and passed without issues, but the engineer did not specifically test the expansion vessel charge at that time. I would rather sort this properly now than keep topping up and risking waterlogging the system.
On the lease question, replacing or recharging an expansion vessel on an existing communal boiler would almost certainly fall within routine maintenance rather than improvement. It is maintaining the existing system in working order, not enhancing or upgrading it. Your lease wording about “heating plant and associated equipment” is fairly standard in converted properties and I would argue an expansion vessel is squarely within that scope.
The trickier issue might be who has the authority to instruct the work. In some leases the freeholder retains responsibility for instructing repairs to communal systems and recovers the cost through the service charge. In others, particularly in smaller conversions where the freeholder is essentially absent, leaseholders end up doing it by mutual agreement and splitting the bill. It depends on whether your lease places a positive obligation on the freeholder to maintain the communal plant or merely passes the cost through.
On the Gas Safe point, any registered engineer can work on the boiler. There is no requirement for it to be the original installer. Worth checking whether your building insurance requires notification of boiler works, though in practice for something this minor it is unlikely to be an issue.
One thing I meant to raise in my earlier reply. The question of who instructs the Gas Safe engineer and who signs off on the work is important in a building with no managing agent. In our situation, the lease assigns responsibility for the communal boiler to the freeholder, but the freeholder is also one of the leaseholders, which creates a slightly odd dynamic where the person commissioning the work is also one of the people paying for it.
Does your lease specify who has the obligation to maintain the communal heating system, or is it silent on it? If it simply says the costs are shared between leaseholders but does not say who actually arranges the work, you could end up in a situation where nobody acts until something fails completely. That is what happened in our building with the guttering, three years of everyone assuming someone else would sort it.
It might be worth the three of you agreeing a simple protocol in writing, even just an email chain confirming who will obtain quotes and how you will agree to proceed. Saves a lot of grief later.
Quick update on this. The expansion vessel was replaced on Wednesday by a Gas Safe engineer I instructed directly. He confirmed the original vessel had failed completely, the diaphragm had perished and it was not holding any charge at all. The system is now holding steady at 1.2 bar after 48 hours which is exactly where it should be for a sealed system with the static head we have in this building.
The vessel itself was a Flamco Flexcon Premium 18 litre, which is the correct match for the ecoTEC plus 838 given the system volume. Total cost was £385 including labour, the old vessel removal and a full system pressure test. He also topped up the inhibitor while he was at it which I thought was reasonable.
The problem now is splitting the cost. There are three flats and the lease says maintenance of shared services is divided equally. The top floor leaseholder has come back saying she does not think she should pay because the boiler “mostly heats the ground and first floor” which is not how a communal sealed system works. The flow and return serve all three flats equally. I have sent her a copy of the relevant lease clause but she is not responding.
@Graspthedetail, given your earlier point about who instructs and signs off, do you think I have any exposure here if she refuses to pay her third? I paid the engineer out of my own pocket and I am now wondering whether I should have got written agreement from all three parties first.
Good news on the repair itself. The fact that it was a failed diaphragm and the system was not holding pressure at all would in most reasonable interpretations constitute urgent maintenance rather than an elective improvement. That distinction matters because it affects whether prior agreement from all parties was strictly necessary before instructing the work.
On the cost recovery question, there are a few things to bear in mind. First, the lease clause requiring equal division of shared service maintenance costs is your primary tool. If it is clearly worded, and it sounds as though it is, then the obligation exists regardless of whether the top floor leaseholder agreed in advance. The argument that the boiler “mostly heats” certain flats is irrelevant to a sealed communal system serving all three properties. Heat distribution may vary due to pipe runs and radiator sizing, but the system itself is shared infrastructure.
Practically, I would do the following. Send a polite written request by email and post, attaching a copy of the invoice, the relevant lease clause, and a brief note explaining that this was urgent maintenance on shared infrastructure. Give her 14 days to respond. If she does not pay, your options are the county court small claims track for her share, which at roughly £128 is straightforward, or, depending on the lease terms, you might be able to set off her share against any future costs where you are collecting collectively.
The fact that you paid up front and instructed the engineer yourself is not ideal from a procedural standpoint, but given the urgency it is defensible. I would not lose sleep over it. Keep all the paperwork and the engineer’s report.