Can You Use the Toilet and Water While a Boiler Is Being Replaced?

Yes, in most homes you can still use the toilet and the cold taps while a boiler is being replaced. The mains water is usually only turned off for short spells while the engineer connects the new boiler, so cold water and toilet flushing work for most of the day. What you lose is hot water and heating for the whole job, and the gas supply for part of it. The exceptions are homes where the toilets fill from a tank in the loft that is being removed, or where the cold water pipework is being rerouted.

Can you use the toilet while a boiler is being replaced?

Usually yes. A toilet cistern fed from the mains refills whenever the mains is on, and the mains is only isolated briefly during most boiler swaps.

If the engineer does turn the mains off, the cistern still holds one flush, and it refills once the water is back on. Ask the engineer to tell you before they isolate the water and roughly how long it will be off; on a like-for-like combi swap it is often under an hour in total, spread across the day. Avoid flushing or running taps while they are working on the cold supply, because it can draw air or debris into the pipes they have just opened.

When might toilets be out of action for longer?

When the job includes removing a cold water storage tank in the loft, which happens when a regular boiler is replaced with a combi. In older London houses, toilets are sometimes fed from that tank rather than the mains.

Before the tank can come out, any toilets, taps or showers it supplies have to be reconnected to the mains. While that work is going on, those toilets may not refill, and it can take a few hours depending on how the pipework runs. The survey should identify which outlets are tank-fed and the engineer should tell you in advance which toilet will stay working. If you are planning this kind of conversion, changing to a combi boiler covers what else is involved.

Will I have hot water during a boiler replacement?

Not from the boiler. Hot water is off from the moment the old boiler is isolated until the new one is commissioned, which is normally the end of the working day on a straightforward swap.

If you have a hot water cylinder that is staying in place and it has an immersion heater, you may be able to keep some hot water. Heat the cylinder fully the night before, and ask the engineer whether the cylinder will stay full during the work; if it is not being drained, the immersion can top it up once the engineer confirms it is safe to switch on. If the cylinder is being replaced as well, there will be no stored hot water until the new system is running. A kettle and an early shower before the engineers arrive cover most households for a day.

Is the gas turned off during a boiler installation?

Yes, for part of the day. The engineer isolates the gas to disconnect the old boiler, and has to carry out a tightness test on the whole gas installation before the new boiler is lit.

That test checks the pipework from the meter to every appliance, so a gas hob or gas fire will not be usable while it is being done. On most jobs the gas is off for a few hours rather than all day, but if the gas pipe to the boiler is being upsized or rerouted, allow longer and plan meals that do not need the hob. Gas work must be carried out by a Gas Safe registered engineer; do not turn the supply back on yourself.

What about heating and electricity?

The heating is off for the whole job, because the system is drained down to swap the boiler. Electricity is normally only isolated at the boiler's own fused spur, so the rest of the house keeps its power.

If a power flush or chemical clean is part of the installation, the heating side takes longer, but it does not affect the cold water or toilets. In winter, keep internal doors shut and have a plug-in heater ready for anyone who feels the cold. Our guide to how long a new boiler installation takes explains how long each type of job usually runs, and one day is typical for a like-for-like swap.

How to prepare the house for installation day

A little preparation keeps the disruption to a minimum and saves the engineers time.

• Ask at the survey which services will be off and for roughly how long, and whether any toilet is fed from a loft tank.
• Shower and fill a kettle before the engineers arrive, and heat the cylinder overnight if you have one with an immersion heater.
• Clear access to the boiler, the gas meter, the loft hatch and the route to the outside wall where the flue goes.
• Keep children and pets away from the work area while the gas and water are open.
• Plan meals that do not rely on a gas hob for the middle of the day.

For a step-by-step view of the day itself, see what happens on boiler installation day. If you would like to know exactly what will be off and when in your own home, book a free survey and it will be set out before the work is booked.