Why can nobody give me an unvented cylinder replacement price over the phone?

Because the cylinder is the predictable part and everything around it is not. The route the discharge pipe takes, whether the old vessel will come out of the cupboard intact, what the mains will deliver and what electrical work is needed all change the hours involved, and none of them can be established from a description. A phone figure is a guess that gets revised on the day.

Is it cheaper to replace a cylinder with the same make and model?

Usually yes, because the connections sit in the same places and the footprint fits the space it came out of. That saves pipework alteration and often saves dismantling the cupboard. It is only the cheaper option if the old cylinder was the right one for the household. Replacing an undersized unit with another undersized unit saves money once and costs it again later.

Does converting from a vented cylinder to an unvented one cost much more?

It is a bigger job than a swap, yes. The loft tank, the cold feed and the vent become redundant and have to be dealt with, a balanced cold take off is normally added, the mains has to be checked for adequate flow, and the wiring usually changes. The result is mains pressure hot water at the outlets, which a like for like vented replacement cannot deliver.

How long does a cylinder replacement take?

A like for like swap in an accessible cupboard is commonly a single day. A conversion from vented to unvented, a loft installation, or a job where the cupboard has to come apart and a long discharge run is needed, can run into a second day. The honest answer on any specific property comes after somebody has seen the space and the route out.

Is the discharge pipe really a significant part of the cost?

It can be. A cylinder sitting against an external wall may need a short run and one core drill. A cylinder in an internal cupboard in the middle of a flat may need a long run with several bends and a considered termination outside. The pipe itself is cheap. Finding a legitimate route for it through an occupied property is what takes the time.

Does hard water in London affect what a replacement costs?

Indirectly. A scaled cylinder takes longer to drain and the sediment in it means the rest of the system is carrying debris too, so flushing and strainer work on the cold side are worth doing at the same time. Hard water does not change the price of the tank. It changes how much surrounding work is sensible while the system is open.

Should I expect to pay for the old cylinder to be taken away?

Removal and disposal are part of the job and should be stated in the quote. That covers the old vessel, any redundant loft tank, old lagging and offcuts. If a quote does not mention disposal, ask, because the alternative is an old cylinder sitting in a garden or a hallway waiting for a second visit.

Will the cupboard need redecorating afterwards?

Usually something needs attention. Shelving and battens often come out, a floorboard may be lifted, boxing rarely fits the new pipe runs, and a new penetration through an external wall needs plaster made good. Most plumbing quotes exclude decoration, which is reasonable, but it should be written down so nobody is surprised by the state of the cupboard on the second day.

What makes one quote much cheaper than another?

Almost always scope rather than rate. The cheaper quote has typically assumed a straight swap, excluded electrical work, not allowed for dismantling the cupboard, or not looked at where the discharge pipe has to go. Put both quotes against the same list of items and the gap usually turns out to be work that has been left out rather than money saved.

Where can I find your actual prices?

On the pricing page. We publish the rate structure there and agree it before we attend rather than writing figures into articles that then go stale. What this page can tell you is which variables move the number on your particular property, so the conversation about cost starts from the right place.

What a Cylinder Replacement Actually Costs

The cost of an unvented cylinder replacement is set by seven things: the capacity and type of cylinder you need, where in the building it sits, how much of the surrounding pipework has to change, how the safety discharge is routed to outside, how hard the old vessel is to remove, whether the controls and wiring have to be reworked, and what is left to make good afterwards. The cylinder itself is usually the smallest surprise on the list. Two flats on the same street can be a clean morning and an awkward two day job, and the difference is almost never the tank. This page walks through each driver in the order an engineer meets it on site, so you can read a quote and tell whether it has been thought about or guessed at. Our own rate lives on the pricing page rather than in this article, because a figure written into prose is out of date the week after it is published.

What drives the cost of an unvented cylinder replacement?

Labour and alteration drive it, not the cylinder. On a like for like swap in an accessible cupboard, where the new unit takes the same connections in the same places, the vessel is the largest single item and the day is predictable. Every step away from that adds hours: a different footprint, a different height, connections on the other side, a discharge pipe that has to find an outside wall, a mains supply that will not deliver enough flow, or a cupboard that has to come apart to get the old tank through the door.

That is why two quotes for the same address can sit a long way apart without either being dishonest. One has assumed a straight swap and the other has walked the route the discharge pipe has to take. The gap is not the profit margin. It is the work one of them has seen and the other has not.

The useful way to think about it is a base job plus a set of variables. The base is: drain and remove the old unit, set the new one, remake the connections, commission it and test. The variables are everything the building does to make that harder. Below is each variable, what triggers it, and roughly how much of the day it tends to take.

Capacity and type of the new cylinder, including whether it is direct, indirect or a thermal store.
Position in the property and the route the old vessel has to travel to leave it.
Pipework changes: mains size, balanced cold take off, secondary return, feed and vent removal.
Discharge pipe routing from the tundish to a safe outside termination.
Electrical work: immersion supply, wiring centre, programmer and valve changes.
Removal and disposal of the old cylinder and any redundant loft tank.
Making good: shelving, floorboards, boxing, plaster and decoration.

Does a bigger cylinder cost much more?

Stepping up a size costs more in material, and the increase between the common domestic capacities is modest against the whole job. What costs real money is when the bigger cylinder no longer fits where the old one stood. A taller unit that fouls a sloping ceiling, or a wider one that will not pass a cupboard door frame, turns a material decision into a joinery decision.

So the honest answer is that capacity is one of the cheaper things to get right and one of the more expensive things to get wrong. Size the cylinder for how the household actually draws hot water, then check the physical envelope before anyone orders anything. Height, diameter, the clearance needed above it to withdraw the immersion heater, and the swing of the cupboard door all matter. An immersion boss with no room to pull the element out is a cylinder that cannot be serviced without partly dismantling the cupboard, and that cost lands later rather than never.

If the current unit runs cold partway through the second shower, replacing like for like preserves the problem and you pay the labour twice. Work out what size hot water cylinder you need before the quote stage, not after the old one is on the landing.

The type of cylinder matters more than the capacity

Changing type is the single biggest cost jump available on this job. Like for like is the cheap version of every scenario below. Direct cylinders heat by immersion element alone. Indirect cylinders carry a coil fed by a boiler. Thermal stores, including the units common in purpose built blocks, work the opposite way round and are not interchangeable with an unvented cylinder without redesigning the plant around them.

Going from a vented copper cylinder to an unvented one is a change of system, not a change of tank. The loft tank, the cold feed and the vent pipe all become redundant. The incoming mains has to have the flow and pressure to feed the whole property at once, and if it does not, the honest answer is either a different solution or an upgrade of the supply. A balanced cold take off is usually added so that showers and mixers see matched pressures. Every one of those is labour.

Cylinders with oversized coils, sold for use with heat pumps, are a further step again, because the pipework and the control strategy differ from a boiler fed unit. None of this is exotic work, but it is not a swap, and a quote that prices it as one has misread the job.

Unvented work is notifiable and has to be carried out by an engineer holding the unvented hot water qualification. That is a fact about who may do the job rather than a cost driver on its own, but a quote that is cheap because the person pricing it does not hold that qualification is not a saving.

Where the cylinder sits decides most of the labour

Position changes the hours more than any other single factor. A cylinder in a ground floor utility room with a door onto the garden is the easy end. A cylinder in a first floor airing cupboard at the top of a narrow return stair is the middle. A cylinder in a loft, reached by a hatch and a ladder, is the difficult end, and it is difficult in both directions because the old one has to come down and the new one has to go up.

Height above the outlets matters too, because the discharge from the safety valves has to fall all the way to a safe termination. A loft installation often needs a long run to reach an outside wall, with every bend counted. A cylinder on the ground floor with an external wall behind it may need a single short run and a core drill.

Then there is the cupboard itself. In a lot of London flats the airing cupboard was built around the cylinder, and the shelving, the batten it sits on and sometimes the door frame have to come out before the vessel will move. That is an hour or two at the start of the day and another hour at the end putting it back, and it is the item most often missing from a quote priced over the phone.

Ground floor with external wall access: shortest discharge run, easiest removal.
First floor airing cupboard: typical London job, often needs the cupboard partly dismantled.
Loft: ladder access both ways, long discharge run, boarding and lighting all matter.
Internal cupboard with no external wall nearby: the discharge route becomes the main variable.

What pipework usually has to change

Assume something changes. Even a like for like swap rarely lines up perfectly, because manufacturers place connections at different heights and on different sides, and the old tails were cut to suit whatever stood there before. A competent quote allows for remaking the hot outlet, the cold feed, the coil flow and return, and the drain point, and for a short length of new pipe at each.

Beyond that, the common additions are a balanced cold take off so the hot and cold sides see the same pressure, an isolating and strainer arrangement on the incoming cold, and a secondary return where the property has one and the new unit needs a different tapping. If the mains coming into the property is old and narrow, flow rather than pressure is usually the limiting factor, and the section from the stopcock to the cylinder may need replacing to get the performance the cylinder is capable of.

Converting from a vented system adds the decommissioning work: capping the old cold feed and vent, removing or isolating the loft tank, and dealing with whatever else that tank was feeding. Some properties run the bathroom cold taps off it, which has to be re-routed rather than abandoned.

Getting the old cylinder out and the new one in

Removal is real work and it belongs in the price. The old vessel has to be drained down, which on a cylinder full of scale and sediment takes longer than the volume suggests, then disconnected, then carried out. A foam lagged unvented cylinder is heavier and more awkward than an old copper one, and neither compresses to fit through a doorway that was framed after it was installed.

Where a vessel genuinely will not come out intact, it is cut down in place, which is noisy, adds time and means covering the route out. That is not a cowboy tactic, it is sometimes the only option in a conversion where a stud wall went up around the cupboard. What matters is that it was foreseen rather than discovered.

Disposal is a line item too. The old cylinder, any redundant loft tank, the old lagging and the offcuts all have to leave the property and be disposed of properly. A quote that does not mention where the old one goes is a quote that has not thought about the end of the day.

Electrics and controls: the part that gets forgotten

Most cylinder replacements involve some electrical work, and it is the element most often left out of a cheap quote. At minimum the immersion supply has to be disconnected and reconnected, and the controls that govern the cylinder have to be reconnected to the new unit. Beyond that it depends on what was there before.

A conversion from vented to unvented usually means new wiring at the cylinder and sometimes a rework of the wiring centre, because the valve arrangement and the safety cut out are not the same as the old setup. A property being taken from a gravity fed layout to a fully pumped one needs motorised valves and a programmer capable of running hot water and heating separately. If the immersion is being fed from an old spur that is no longer suitable, that is work for a qualified electrician and it needs to be priced, not assumed.

Ask any quote to say explicitly what electrical work is included. The answer separates the people who have surveyed the job from the people who have priced a tank and a day.

Making good: what a replacement leaves behind

Making good is a separate trade and it is fair for a plumbing quote to exclude it, but it should say so. Expect the cupboard to look worse afterwards than it did before, because the shelving came out, the batten was cut, the pipework now runs where the old runs did not, and a core drill has gone through an external wall.

The predictable items are: shelving and battens refitted or renewed, a patch of floorboard or chipboard lifted and screwed back, a boxed section that no longer fits its old pipework, plaster made good around any new penetration, and a coat of paint in the cupboard. None of it is expensive on its own. All of it adds up if you assumed it was included.

The item most worth asking about specifically is the external termination of the discharge pipe, because that is the one that is visible from the street or the garden. Where it comes out, what it looks like and how it is finished are worth agreeing before the drill comes out rather than after.

Get the exclusions in writing. A quote that covers the cylinder, the pipework and the commissioning but not the decorating is perfectly normal. A quote that is silent on the subject and then produces a second bill is not.

Why the same job costs differently across London

The building stock explains most of the variation, and it splits into three broad cases. Victorian and Edwardian conversions typically have the cylinder in a first floor cupboard, with pipework boxed into a corner and altered several times, and no external wall conveniently behind it. Purpose built blocks often have a thermal store rather than a cylinder, sized to a cupboard that was designed around it, which makes a like for like unvented cylinder a design question rather than a swap. Newer builds usually have an unvented cylinder already, frequently tied into underfloor heating with liquid screed and a manifold, so the controls and the zoning come into the job alongside the tank.

The water does the rest. Almost the whole London supply area is hard, so an old cylinder coming out is generally coming out full of scale and sediment, which lengthens the drain down and means the debris that has been circulating is still in the system. Flushing and strainer work on the cold side is worth doing at the same time, because the alternative is that the same grit settles on the seat of a new valve.

None of this makes a London job unusual. It makes it worth surveying. The variation is between properties rather than between postcodes, which is precisely why a price quoted from a description on the phone tends to be wrong in one direction or the other.

How to compare two cylinder replacement quotes

Compare scope before you compare figures. Two quotes that differ by a wide margin are usually pricing two different jobs, and the cheaper one is often the one that will grow. Put both on the same list of questions and the comparison becomes straightforward.

The questions that separate them are all about what has been allowed for rather than what the cylinder costs. If one quote names the make, model and capacity of the unit, states the discharge route, says who is doing the electrical work and lists what is excluded, and the other is a single number with the word cylinder next to it, you are not looking at two prices for the same thing.

Our rate structure sits on the pricing page and is agreed before we attend, and we do not price a cylinder replacement from a description over the phone, because the variables above are the job. Twenty engineers see a lot of cupboards, and the one consistent lesson is that the survey is what makes the number hold.

Which cylinder: make, model, capacity, direct or indirect.
Where the discharge pipe runs and where it terminates outside.
What pipework alterations are included, including any balanced cold take off.
Who does the electrical work and whether it is in the price.
Whether removal and disposal of the old cylinder and any loft tank are included.
What making good is included and what is explicitly excluded.
Whether commissioning and handover of the paperwork are included.

Questions we get asked

Why can nobody give me an unvented cylinder replacement price over the phone?: Because the cylinder is the predictable part and everything around it is not. The route the discharge pipe takes, whether the old vessel will come out of the cupboard intact, what the mains will deliver and what electrical work is needed all change the hours involved, and none of them can be established from a description. A phone figure is a guess that gets revised on the day.
Is it cheaper to replace a cylinder with the same make and model?: Usually yes, because the connections sit in the same places and the footprint fits the space it came out of. That saves pipework alteration and often saves dismantling the cupboard. It is only the cheaper option if the old cylinder was the right one for the household. Replacing an undersized unit with another undersized unit saves money once and costs it again later.
Does converting from a vented cylinder to an unvented one cost much more?: It is a bigger job than a swap, yes. The loft tank, the cold feed and the vent become redundant and have to be dealt with, a balanced cold take off is normally added, the mains has to be checked for adequate flow, and the wiring usually changes. The result is mains pressure hot water at the outlets, which a like for like vented replacement cannot deliver.
How long does a cylinder replacement take?: A like for like swap in an accessible cupboard is commonly a single day. A conversion from vented to unvented, a loft installation, or a job where the cupboard has to come apart and a long discharge run is needed, can run into a second day. The honest answer on any specific property comes after somebody has seen the space and the route out.
Is the discharge pipe really a significant part of the cost?: It can be. A cylinder sitting against an external wall may need a short run and one core drill. A cylinder in an internal cupboard in the middle of a flat may need a long run with several bends and a considered termination outside. The pipe itself is cheap. Finding a legitimate route for it through an occupied property is what takes the time.
Does hard water in London affect what a replacement costs?: Indirectly. A scaled cylinder takes longer to drain and the sediment in it means the rest of the system is carrying debris too, so flushing and strainer work on the cold side are worth doing at the same time. Hard water does not change the price of the tank. It changes how much surrounding work is sensible while the system is open.
Should I expect to pay for the old cylinder to be taken away?: Removal and disposal are part of the job and should be stated in the quote. That covers the old vessel, any redundant loft tank, old lagging and offcuts. If a quote does not mention disposal, ask, because the alternative is an old cylinder sitting in a garden or a hallway waiting for a second visit.
Will the cupboard need redecorating afterwards?: Usually something needs attention. Shelving and battens often come out, a floorboard may be lifted, boxing rarely fits the new pipe runs, and a new penetration through an external wall needs plaster made good. Most plumbing quotes exclude decoration, which is reasonable, but it should be written down so nobody is surprised by the state of the cupboard on the second day.
What makes one quote much cheaper than another?: Almost always scope rather than rate. The cheaper quote has typically assumed a straight swap, excluded electrical work, not allowed for dismantling the cupboard, or not looked at where the discharge pipe has to go. Put both quotes against the same list of items and the gap usually turns out to be work that has been left out rather than money saved.
Where can I find your actual prices?: On the pricing page. We publish the rate structure there and agree it before we attend rather than writing figures into articles that then go stale. What this page can tell you is which variables move the number on your particular property, so the conversation about cost starts from the right place.