How We Rebuilt the Hot Water System in a Six-Room Liverpool HMO
- 2 days ago
- 9 min read
Six showers. Six kitchens. One ordinary domestic electricity supply, and no stored hot water anywhere in the building.
That was the specification we were called to look at in a six-room house in multiple occupation in north Liverpool earlier this summer. Every room had its own bedroom, kitchenette and shower room, and every drop of hot water in the property was being heated instantaneously, on demand, by electricity. On paper it looked like a tidy conversion. In practice, the boards were tripping, the pressure was poor, and the tenants had gone.
The calculations nobody did until DD Wilson Gas And Heating Engineers quoted.
An instantaneous electric shower is a large appliance. A single unit commonly sits somewhere between 7.5kW and 10.5kW. One of them in a family home is perfectly normal.
Six of them, in a building where six unrelated households come and go on their own schedules, is a different proposition. If four tenants happen to shower between seven and nine on a weekday morning, the building is asking for something in the region of 34kW from the shower circuits alone, before anyone has boiled a kettle or switched a light on.
A typical single-phase domestic supply is rated at 60A, 80A or 100A. At 230V, an 80A supply gives you roughly 18kW for the entire property. The numbers do not meet in the middle, and no amount of good workmanship downstream will make them meet.
So the boards tripped. Repeatedly. The tenants dealt with weak showers and an electricity supply that kept cutting out. Then they left.
Why the cheap version costs more
The original conversion had been done to a budget. That is not unusual, and it is not, in itself, wrong. What went wrong here was that nobody modelled how the building would actually be used before the pipework and the cabling went in.
We see the same pattern often enough that we have written about it before, in our account of restoring a botched heating installation and in our warning about what happens when an outdated system is left in place too long. A specification that suits one household rarely survives contact with six.
The new owners are long-standing customers of ours. They took the property on knowing it needed doing once and doing properly, and they called us the same week.
What we installed
Two Telford Tempest direct unvented stainless cylinders, 250 litres each. One per floor. Five hundred litres of stored hot water in a building that previously stored none, feeding new hot and cold supplies to every tap, every kitchen sink and every shower in the property. Each cylinder is heated by a single 3kW immersion element.
That is the number that matters. The building has gone from a potential peak demand of thirty to fifty kilowatts for hot water down to six. Roughly the same energy still goes into heating water over the course of a day. It simply goes in gradually, gets stored, and comes back out on demand instead of being pulled from the grid in a twenty-minute rush every weekday morning.
The electrics stopped tripping because the load stopped spiking. That is the whole fix, and it is why unvented systems keep turning up in shared houses.
Mains pressure at every outlet
Unvented cylinders run at mains pressure. The incoming static cold water pressure at this property is 3 bar, and the system was commissioned to deliver at it. Every shower in the building, rain heads included, and every sink was run and checked at handover. The pressure held. If you have ever dealt with low water pressure in a property, you will know how much difference that makes to how a room feels to live in. Poor pressure was one of the two things that emptied this building.
Why two cylinders and not one
A single large cylinder would have stored the same volume of water. It would have been cheaper to buy and quicker to fit. We specified two anyway.
One failure should not empty a building
We fitted a bypass link between the two cylinders. If one goes down, the owner opens the bypass, and the remaining cylinder carries both floors until the other is back in service.
Work out what a single cylinder failure actually costs in a six-let property. An element or a thermostat is a cheap part. But if it is not on the van, it might be the next day, and if it turns into a warranty claim, it can be longer than that. Meanwhile, six households have no hot water and at least one of them starts looking at other rooms. A six-room Liverpool HMO running its hot water system through one component is six rents riding on one part.
With a bypass, that failure becomes an inconvenience instead of six sets of notice. The owner opens one valve. Everybody still gets a shower while we sort the other cylinder out.
Each cylinder also has its own cold feed isolation valve, so either can be worked on without draining or shutting down the other. A service visit does not have to become a whole-building event, which matters when you are trying to get access to six occupied rooms on the same afternoon.
Short pipe runs beat long ones
Storing hot water on the floor it serves keeps the pipe runs short. Tenants wait less time at the tap, less water goes down the drain waiting for it to run hot, and every room behaves the same way. Nobody is stuck at the end of a long dead leg wondering why their shower is worse than the room next door.
Room to grow
The pressure-reducing valves have been capped off, so a balanced cold feed can be taken off elsewhere later without disturbing anything already installed.
We quoted to strip out the bathrooms. Then we found another way.
Getting new hot and cold supplies to six separate shower rooms means getting pipework to six separate shower rooms. When we first priced the job, the honest answer was that the bathrooms would have to come out to route it. That is a serious number on top of the installation, and it is weeks of extra work before any of those rooms can be let again. Our installation team looked at it again on site and found another route. The new supplies went in through the backs of the bathroom walls, so the finished rooms stayed where they were. The only openings we made were at the points where the old showers and their cabling came out, and those were filled and left ready for the decorator. The client saved a substantial sum against our original quotation and got the property back towards a lettable condition considerably faster. An in-depth plumbing survey exists to catch exactly that, before anyone prices anything.
Where a property genuinely does need the rooms taken
back to brick, we handle that too through our full bathroom installation service. In this case it was not needed, and saying so was worth more to the client than the extra work would have been worth to us.
Certification and commissioning
Unvented hot water is stored under mains pressure. It is notifiable work under the Building Regulations, and it can only legally be installed and commissioned by an operative holding the relevant unvented hot water qualification, usually referred to as G3.
Both cylinders here were commissioned on 24 July 2026, and a Benchmark Mains Pressure Hot Water Storage System Commissioning Checklist was completed for each and left with the customer. The record confirms:
The combined temperature and pressure relief valve and the expansion valve fitted and discharge tested
Tundish and discharge pipework connected and terminated in accordance with Part G of the Building Regulations
Energy sources fitted with a cut-out device
Expansion vessel checked
Incoming static cold water pressure recorded at 3 bar
Pipework insulated to the point of concealment
Controls demonstrated to and understood by the customer
If you own an unvented cylinder and nobody has ever serviced it, that paperwork matters more than most landlords realise. We have written separately on the risks of a neglected unvented cylinder, and we do unvented cylinder servicing across Merseyside.
Why this matters for Liverpool landlords right now
Liverpool's current landlord licensing scheme runs until March 2027, and the council is consulting on what replaces it. The consultation closes on 5 October 2026, and one of the options on the table would extend selective licensing across all 64 wards in the city.
The council's own figures give a sense of how active enforcement has become. Since the current scheme launched in April 2022, more than 19,000 inspections have been carried out, uncovering over 3,500 housing hazards and leading to more than 1,100 enforcement notices. Property condition is not a paperwork exercise in this city any more. If your portfolio includes converted properties, this is a sensible year to know what is actually behind the walls. Our landlord certificate service and our wider safety certificate work exist for exactly that reason, and our earlier guidance for landlords concerned about tenant safety still applies.
Questions worth asking about your own property
If you own, manage or let a converted property, these are worth twenty minutes of somebody's time before anything goes wrong.
What happens to your supply if every shower in the building runs at once? Add up the ratings. Compare it to your main fuse. If the answer makes you wince, that is useful information.
Is there stored hot water, and is it near the outlets it serves? Storage flattens demand and shortens pipe runs. Both matter more as occupancy rises.
When was the electrical installation last inspected, and does the certificate cover the load that is on it today? Conversions change the load. Certificates do not update themselves.
If you cannot answer all three, book a survey.
Frequently asked questions
What size hot water cylinder does an HMO need?
It depends on the number of lettable rooms, the number of showers, and how those showers are likely to be used at the same time. Sizing for total occupancy alone will get you into trouble, because what matters is simultaneous demand, not the headcount on the tenancy agreements. In this six-room property, we specified 500 litres across two 250-litre cylinders. Every building is different, and it is worth having it calculated properly.
Do I need a G3 qualified engineer to install an unvented cylinder?
Yes. Installing or commissioning an unvented hot water storage system over 15 litres requires the relevant unvented hot water qualification, and the work is notifiable under the Building Regulations. Ask to see the qualification before anyone touches the cylinder. Any competent engineer will hand it over without hesitation.
Why fit two cylinders instead of one big one?
Resilience and pipe runs. Two cylinders linked by a bypass mean a single failure does not leave the whole building without hot water, and siting storage on the floor it serves keeps the runs short so every room gets hot water quickly and at even pressure. In a property where six separate rents depend on the system, that redundancy is usually worth the extra cost.
How much does an HMO hot water system cost in Liverpool?
There is no useful single figure, because the cost is driven by how many rooms need supplying, how far the pipework has to travel, what the existing electrical installation can carry, and how much making good is involved. The honest answer is that a survey costs you nothing and gives you a real number. Request a quick quote or book online and we will come and look.
Will I have to strip out the bathrooms to fit a new system?
Sometimes, but far less often than people expect. On this project we quoted on that basis and then found a route through the backs of the walls that avoided it almost entirely. It is always worth having someone look properly before you accept that the rooms have to come out.
Do you work on commercial properties as well as HMOs?
Yes. We work with landlords, letting agents, facilities managers, care homes and student accommodation providers across Merseyside and the North West. Our commercial gas engineers handle everything from commercial boiler servicing to full system design, and our local areas page lists everywhere we cover.
Can you fix pressure problems without replacing the whole system?
Occasionally. Poor pressure can come from a partially closed valve, a blocked strainer, scale, or a leak, and those are cheap to put right. It can also be a design problem, in which case no amount of tinkering will fix it. Our general plumbing and leak detection teams will tell you which one you have got.
Talk to us about your property
Own or manage an HMO, a block, a care home or student accommodation?
DD Wilson Gas And Heating Engineers Ltd has been working across Liverpool, Merseyside and the North West since 1998. We design, install and maintain hot water systems built for the way a building is actually used, and we will tell you honestly whether what you have got is fit for it.
Call: 0151 739 8945
Email: info@ddwilson.com
Book a survey: Book online or request a quick quote
Or visit our contact page
Gas Safe registered 583586. Companies House 14258693. Vaillant Advance Master Technician, ATAG approved installer and Panasonic PRO Partner. Over 2,498+ reviews at an average of 4.9 stars. Read our testimonials.
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Written by the team at Constellation Marketing Solutions and DD Wilson Gas And Heating Engineers Ltd. Installation and commissioning carried out by our engineers in July 2026. Property details have been kept general at the owner's request.
