Removal of water storage tank

With a typical electric water heater mounted on a wall, the work follows a clear order. It looks simple at first, but each step is there for a reason:

1. Switch off the circuit breaker for the water heater and check that the supply cable is dead.
2. Close the cold water supply to the water heater.
3. Open a hot tap in the home so that air can get into the tank and the water can flow out.
4. Drain the tank through the drain valve or with a hose into a drain.
5. Disconnect the cold and hot water connections and cap them off.
6. Disconnect the electrical supply and terminate it safely.
7. Lift the empty water heater off its bracket, ideally with two people.
8. Check the condition of the valves, the pipework and the wall fixings.

Why does the tank have to be drained first? A full tank weighs roughly one kilogram for every litre it holds, plus the weight of the unit itself. Taking it down full is dangerous for the people lifting it and for the wall. Draining a larger tank also takes a while, especially if limescale has partly blocked the drain outlet.

If the water heater is hard-wired rather than plugged into a socket, a qualified electrician has to disconnect the supply and make it safe. If the unit hangs high up or above a bath, the work means handling a heavy load from a ladder, so a non-professional should not do it alone.

Gas water heater

With a gas water heater, the gas supply and the flue need attention as well as the water. Only a qualified, registered gas engineer may disconnect a gas appliance. The engineer shuts off the gas, disconnects the appliance, caps the gas pipe and checks that it is tight. They also disconnect the flue pipe and either seal the opening into the chimney or prepare it for the new appliance. You should receive written confirmation of the work.

If you smell gas during the work or at any time afterwards, do not use light switches or naked flames. Open the windows, leave the room and call your gas emergency line or the emergency number 112.

Cylinder heated by a boiler

An indirect hot water cylinder has a coil inside that is connected to the heating circuit. Before removal, the heating engineer has to isolate the circuit with valves or drain the water from the heating system. Otherwise water ends up on the floor and air gets into the system. Once the new cylinder is fitted, the heating is refilled, bled and topped up to the pressure stated by the boiler manufacturer. If draining the whole system is not practical, for example in winter in an occupied house, the heating engineer sometimes uses pipe freezing. A special device creates a temporary ice plug in the pipe so that only the necessary section has to be disconnected.

Large and floor-standing cylinders

Floor-standing cylinders in a boiler room are heavy and often sit in a narrow room or a cellar reached by stairs. For these, the route out, protection for floors and door frames and the number of people needed to carry the cylinder are planned in advance.

The amount of work varies from home to home. It is easier if:

• The water heater hangs in an accessible place at a reasonable height
• The isolation valves work and close tightly
• The unit has a plug or a clearly labelled circuit breaker
• You can hand in the old unit straight away when buying the new one

It takes more time and effort if:

• The fittings are corroded and cannot be undone without cutting
• The cold water valve does not shut off fully and the water has to be turned off for the whole flat or house
• In a block of flats, the riser has to be shut off, which you arrange beforehand with the building management or owners' association
• It is a gas appliance or a cylinder connected to the heating
• The tank is large, stands in a hard-to-reach room or hangs high up
• Pipework has to be altered, valves replaced or the wall strengthened for the new unit at the same time

In practice it often turns out that the old valves and the safety valve are clogged after years of use. The installer will usually recommend replacing them before the new water heater goes up, so there is no need to come back to that wall later.

An electric water heater counts as electrical waste, so do not put it in your household waste bin. You can take it to your local recycling centre, or hand it back to the shop when you buy a new appliance, as retailers usually offer take-back. Scrap metal dealers also accept gas water heaters and steel cylinders. Many companies that remove water heaters will take the old one away too. Agree this in advance so the empty tank does not end up standing in your hallway.

If the removal involves moving a gas appliance, changing the chimney or altering load-bearing parts of the building, check with your local building authority whether the work needs to be notified or approved under local building regulations. Simply replacing a water heater in the same place is normally routine maintenance, but for bigger changes it is wiser to ask first.

• The water heater is taken down while still full or only partly drained
• No hot tap is opened during draining, so the water barely flows
• The power is switched off only at the thermostat, not at the circuit breaker
• The water connections are left uncapped after disconnection, so a single turn of the main stopcock causes a flood
• Someone without the right qualification disconnects a gas appliance
• Bleeding and system pressure are forgotten on a cylinder connected to the heating
• In a block of flats, the water is shut off for the whole building without any arrangement

Before the installer leaves, go through these points:

• The cold and hot water connections are capped and the area below them is dry
• The main stopcock is open again and nothing is dripping
• The electrical supply is safely terminated and the circuit breaker is labelled
• For a gas appliance, you have written confirmation of capping and the tightness test
• The opening into the chimney is sealed or prepared for the new appliance
• The heating is refilled, bled and the pressure matches the boiler manufacturer's figure
• The wall and brackets are in a suitable condition for the new water heater
• The old tank has been taken away or you know where to take it