Usually, yes. If you are converting from a system or regular boiler to a combi, the hot water cylinder is normally removed or taken out of use. A combi heats water on demand, so it doesn’t need a storage cylinder. If your home already has a combi, there is no cylinder to remove.
The exact work depends on your current setup, your water supply, and how much hot water your household uses. A Gas Safe registered engineer should check these before confirming a conversion.
Do You Have to Remove the Hot Water Cylinder for a Combi Boiler?
Yes, in most full conversions the cylinder is no longer needed, so it is removed or decommissioned. A combination boiler heats water straight from the mains when you open a tap. A cylinder does the opposite: it heats water in advance and stores it. With a combi, the cylinder has no job left.
It helps to know which kind of project you have:
- Combi-to-combi replacement. You already have a combi. There is no cylinder, so nothing to remove.
- System boiler to combi. You have a boiler plus a hot water cylinder, usually in an airing cupboard. The cylinder becomes redundant.
- Regular (conventional) boiler to combi. You have a boiler, a cylinder, and usually tanks in the loft. The cylinder and the loft tanks both become redundant.
Installers sometimes use the word “conversion” for the second and third cases. It takes more work than a straight swap because the pipework changes as well as the boiler.
What Happens to Your Existing Hot Water Cylinder?
The engineer drains it, disconnects it, and either removes it or leaves it safely isolated. In most London homes, removal is the better choice because the cylinder takes up valuable space.
Draining and disconnecting the cylinder
The engineer shuts off the water supply to the cylinder, drains it, and disconnects the pipes. Cylinders are heavy when full and connected to both water and heating pipework, so this is not a DIY job.
Removing the cylinder or leaving it in place
An unused cylinder does nothing useful. It takes up space and can still have live connections if it’s not isolated properly. Most homeowners choose to have it taken out, which also frees up the cupboard. Ask your installer whether disposal is included in the quote.
What happens to the immersion heater and old pipework?
The immersion heater is part of the cylinder, so it goes when the cylinder goes. If it’s wired to a switch or fused spur, the electrical side should be made safe. The old hot and cold pipes are either removed or capped and isolated. Redundant pipework shouldn’t be left live or dangling.
Do You Need to Remove the Loft Tanks as Well?
Only if your home has them, and it depends on the system you have now. Different systems have different tanks:
| Existing system | Hot water cylinder | Loft tanks |
|---|---|---|
| Regular (conventional) boiler | Yes | Usually a cold-water storage tank and a feed and expansion tank |
| System boiler | Yes | Usually none, because the expansion vessel is built into the boiler |
| Existing combi boiler | No | No |
After a conversion to a combi, a sealed heating system and mains-fed hot water make the loft tanks redundant. Many homeowners have them removed to free up loft space and reduce the risk of leaks or frozen pipes. Removal isn’t always automatic, so confirm it is included in your quote.
Can You Keep a Hot Water Cylinder With a Combi Boiler?
Not normally. A standard combi doesn’t need one, and keeping it adds no benefit in a typical conversion. A combi is built to heat water as you use it. Connecting it to a storage cylinder would mean a specially designed system, which is unusual in homes.
If you want stored hot water, you have better options than a hybrid setup:
- Keep a system boiler with an unvented cylinder.
- Choose a different boiler type, designed around storage.
When is keeping a cylinder worth considering?
Think about keeping stored hot water if:
- Several people regularly shower at the same time.
- You have three or more bathrooms.
- Your mains water flow is weak.
- You want hot water to keep working during a boiler fault, using an immersion heater as a backup.
Is a Combi Boiler Right for Your London Home?
A combi suits many London flats and smaller houses, but not every home. The question isn’t only “can the cylinder come out?” It’s whether a combi can serve your hot water needs without the cylinder.
Small houses and flats
For one- and two-bedroom homes, a combi is often a good fit. You get a hot water supply with no storage tank, plus a cupboard back. Space is tight in most London flats, so this matters.
Larger family homes and multiple bathrooms
A combi serves one or two outlets well. Run two showers at once in a large house and the flow can drop for both. A system boiler with a suitably sized cylinder often copes better with this kind of demand.
Older and Victorian London properties
Victorian and Edwardian terraced houses often have older pipework, awkward boiler locations, and tight cupboards. These aren’t reasons to avoid a combi. They are reasons to inspect the property before quoting. Check pipe condition, the flue route, the condensate drain, and the incoming water supply.
What Should an Engineer Check Before Recommending a Conversion?
A good engineer will check your water supply, your hot water demand, and your existing pipework before recommending anything. Expect these checks:
- Mains water pressure and flow rate. Combi boilers rely on the incoming mains. Manufacturers publish minimum requirements, so measure rather than guess. Many London homes are supplied by Thames Water, and local supply conditions vary.
- How many people use hot water, and when. Morning showers back to back are the real test.
- Your existing set-up. Boiler type, cylinder, tanks, and where each pipe runs.
- Gas pipe size. A combi can demand more gas than your current boiler, so the supply pipe must be able to deliver it.
- Flue position and condensate drainage. The boiler must vent safely and drain properly.
- Heating demand. The boiler output must match the home’s needs.
- Manufacturer instructions and compliance. The installation should follow the maker’s instructions and Building Regulations, and the engineer should complete commissioning paperwork, such as the Benchmark checklist.
If the survey shows a combi won’t perform well, a good installer will say so and offer an alternative.
What Happens During a System-to-Combi Conversion? (Step by Step)
A conversion usually follows the same sequence, though details vary from home to home.
- Survey and quote. The engineer inspects the existing system and agrees the plan.
- Drain down. The heating system and cylinder are drained.
- Remove old components. The old boiler, cylinder, and any redundant tanks are disconnected and taken out.
- Alter pipework. Hot and cold water pipes are reconfigured for the combi. Heating flow and return pipes are adjusted if needed.
- Fit the new boiler. It is mounted, with the flue, gas supply, and condensate pipe connected.
- Clean and protect the system. The heating circuit is flushed, and inhibitor is added to protect against corrosion and sludge.
- Fit controls. A thermostat or smart controls are installed.
- Commission and test. The engineer fills, tests, and checks the system, then completes the commissioning documents.
- Hand over. You get an explanation of the controls, plus warranty details.
How long does it take?
A conversion generally takes longer than a like-for-like swap because there is more to disconnect and re-plumb. Many are completed in one to two days, though larger or more complex jobs can run longer. Ask your installer for an estimate based on your property: [insert your typical timescale].
How Much Does It Cost to Remove a Cylinder and Install a Combi in London?
The cost depends on the property, so there is no single London price. A conversion costs more than a straight combi swap because of the extra work.
A good quote should itemise:
- The combi boiler and installation labour
- Cylinder removal and disposal
- Loft tank removal, if applicable
- Pipework alterations
- Flue and condensate pipe work
- System cleaning and inhibitor
- Heating controls
- Commissioning and paperwork
- Making good after the work
What can make the conversion more expensive?
- Moving the boiler to a new position
- Long or difficult pipe runs
- Tight access, such as flats with limited space
- Old or damaged pipework
- A gas supply pipe that needs upgrading
- A heating system in poor condition
- Extra decorating or making good
Is cylinder removal included in the quote?
Don’t assume it is. Ask these questions in writing:
- Is cylinder removal and disposal included?
- Are loft tanks removed or just disconnected?
- Who makes good the airing cupboard and pipework?
- Is the gas pipe size checked and, if needed, changed?
Should You Remove the Cylinder or Keep Your Existing System?
Remove it if your household is small to medium and your water supply is good. Keep stored hot water if you have high demand or weak mains flow.
| Combi (no cylinder) | System boiler with cylinder | |
|---|---|---|
| Space | Frees up the airing cupboard | Needs cupboard space |
| Hot water supply | On demand; won’t run out | Limited to what’s stored, then recovery time |
| Two showers at once | Can struggle | Usually copes better |
| Mains reliance | High; needs good pressure and flow | Lower with a standard cylinder; unvented cylinders need good mains |
| Installation work | More work to convert | Simple if already in place |
| Best for | Flats and small to medium homes | Larger households and multiple bathrooms |
Neither option is better for every home. The right choice depends on the people who live there and the water supply you have.
Frequently Asked Questions
Do I need to remove the hot water cylinder when installing a combi boiler?
Usually, yes, when converting from a system or regular boiler. A combi heats water on demand, so the cylinder is redundant. If you already have a combi, there is no cylinder to remove.
Can a combi boiler work with a hot water cylinder?
A standard combi doesn’t need one. Specially designed systems can combine the two, but this is unusual and needs a design specific to the equipment.
What happens to the immersion heater when the cylinder is removed?
It goes with the cylinder. The electrical connection should be made safe by a qualified person.
Do loft water tanks need to be removed too?
If you have a regular boiler, the cold-water storage tank and feed and expansion tank become redundant after conversion. They are often removed, but confirm this is in your quote.
Will removing the cylinder affect my radiators?
Not directly. Heating pipework may need alterations, and the system should be cleaned and balanced during the conversion.
Can a combi boiler run two showers at once?
It can struggle. Performance depends on your mains flow rate and the boiler’s output. Two showers are often too much for a typical combi, particularly with weak water flow.
Will a combi boiler improve my water pressure?
Not necessarily. A combi delivers water at roughly your mains pressure, so it can feel strong in some homes and weak in others.
Can a combi conversion be done in a London flat?
Often, yes, and flats tend to benefit from the saved space. The engineer must check the flue route, the condensate drain, and any lease or building rules.
Do I need new radiators when converting to a combi?
Not usually. Existing radiators are often reused if they are in good condition and the system is cleaned properly.
Do I need a Gas Safe registered engineer?
Yes. By law, gas work must be done by a Gas Safe registered engineer. You can check an engineer’s registration on the Gas Safe Register website.
Conclusion
If you’re converting from a system or regular boiler to a combi, the hot water cylinder is usually removed. Loft tanks, if you have them, typically go too. That frees up space and simplifies your heating system. The part that matters most is the survey: your water pressure and flow, your household’s hot water habits, and the condition of your existing pipework decide whether a combi is a good idea at all.
Not sure whether your home suits a combi? Book a boiler conversion assessment with our London team. We’ll inspect your system, check your water supply, explain what would be removed, and give you a clear written quote.