Checks to Make Before Calling a Boiler Engineer

If your home has been flooded and you have no heat or hot water, the first thing to know is that you should not switch the boiler back on to find out whether it still works. Official flood guidance is consistent: make sure your gas and central heating has been checked by an engineer before turning it on¹. The same applies to oil systems, and to the electrics that power the boiler and its controls.

The order matters. Gas and electricity supplies should stay switched off until a qualified professional has checked the systems thoroughly². Get your utilities company or a qualified engineer to check they are safe before turning them back on³. For the wiring, wait for an electrician's approval before restoring power, and do not use electrical equipment exposed to flood water until a qualified electrician has checked it⁴.

Once those checks are done, the boiler can be brought back into use, and the heating can then help dry the house. This page sets out the checks in the order to make them, what each one covers, and how to confirm that the person you call is genuinely qualified for the work.

The checks to make, in order

Work through this list before you ring anyone, so that you can tell the engineer exactly what has happened and what has already been done.

1. Keep the gas and electricity off. Supplies should remain switched off until a qualified professional has checked the systems thoroughly². If the electricity supply is not already off at the mains, get a qualified person to switch it off, and do not touch sources of electricity while standing in flood water⁹.
2. Note what got wet. Which rooms flooded, how deep the water came, and whether it reached the boiler, the controls, the wiring or any appliance. This decides what needs checking.
3. Ring your gas, electricity and water companies. You will need to have your supplies checked before you switch them back on¹⁰. Your personal flood plan should note that you may need gas or electricity engineers to check your supply before turning it back on¹¹.
4. Book a Gas Safe registered engineer for the gas side. If you use gas heating or gas appliances, you will need a Gas Safe registered engineer to do an inspection after a flood¹².
5. Book a registered electrician for the wiring. Ask for an Electrical Installation Condition Report (EICR) on your home, which checks the condition of the electrical wiring, and ask the electrician to check any electrical equipment or appliances affected by floodwater¹⁰.
6. Have the boiler and heating checked before it is switched on. Gas or oil central heating should be checked by a qualified person before you switch on the gas or try to light any appliance⁴.
7. Only then restore the supply and run the heating. Once the system has been checked, you can use the central heating to help dry the house⁷.
8. Fit or check a carbon monoxide detector. Official guidance is to be aware of the signs of carbon monoxide poisoning and always ensure your property has a carbon monoxide detector⁸.

Leave gas and oil heating off until an engineer has checked it

The single most important rule after a flood is that the boiler stays off until someone qualified has looked at it. Gas or oil central heating should be checked by a qualified engineer before turning it on¹³. Gas and oil central heating should be checked by an engineer, and electrics by a qualified electrician, before they are turned back on¹⁴. Do not turn on gas or gas appliances until your system has been checked by a Gas Safe registered engineer¹⁵.

This is not box ticking. Water gets into places you cannot see: the flue, the burner, the controls, the fuel line on an oil system. A boiler that lights and appears to run can still be unsafe. That is why the advice is to have your gas or oil central heating checked by a qualified person before switching on the gas or trying to light any appliance⁴, and why a gas engineer should evaluate safety before you use gas appliances, with no attempt to turn them on if damage or leaks are suspected¹⁷.

Oil systems deserve particular care. The same rule applies: get gas or oil central heating checked by a qualified engineer before turning it on¹³. If you want to understand how an oil boiler behaves when it locks out or runs dry, that is covered separately in the oil boiler breakdown guidance, but none of those steps replace the post-flood inspection.

For appliances that use fossil fuels, including wood, the wider advice is to have them installed and serviced at least annually by a qualified and registered engineer, and not to turn on appliances which may have got wet until they have been checked¹². After a flood, that annual service is the minimum, not the answer.

Electrics need a qualified electrician before they go back on

The boiler depends on the electrics, and flooded electrics are a danger in their own right. Wait for an electrician's approval before turning power back on⁴. Do not use electrical equipment that has been exposed to flood water until a qualified electrician has checked it, and properly switch off all electrical appliances before the supply is restored⁴.

Ask for an EICR. A registered electrician will check the condition of the wiring, and can also check any electrical equipment or appliances affected by floodwater¹⁰. If you know or suspect that electrical equipment associated with a private water supply has been affected, it should be inspected and declared fit for use by a suitably qualified electrician before you try to restore the supply¹⁸. The same principle applies to anything electrical in the house.

Heating appliances get their own warnings. If you think the wiring is damaged, do not use your heater: get it checked by a qualified electrician¹⁹. If you find any damage, or are not sure about the fuse or wiring, get a qualified electrician to advise you²⁰. Fixed electric heaters should be installed by a qualified electrician²¹. And if a heater is electrical and getting older, get it tested by a qualified electrician or replace it²².

If you cannot get a satisfactory answer from a competent electrical contractor about a safety concern, the Health and Safety Executive advises contacting HSE²³.

Turning the heating on to dry the house, once it is safe

Drying out is the reason most people want the heating back on quickly, and once the checks are done it is exactly what the heating is for. You can use your central heating to help dry out the house once the heating system has been checked by a qualified engineer⁷. For best results, set the temperature at 20 to 22 degrees centigrade⁷. Keep the thermostat between 20°C and 22°C for steady drying⁹.

How you dry depends on the method. If you are drying naturally, keep doors and windows open as much as possible. If you are using dehumidifiers, close external doors and windows instead. If the gas or oil central heating has been checked by an engineer, turn it on and keep the thermostat between 20°C and 22°C for steady drying⁹.

Ventilation is not optional. Ensure heaters, dryers or fires are well ventilated to avoid carbon monoxide poisoning, and do not use petrol or diesel generators or other similar fuel-driven equipment indoors, because their exhaust gases contain carbon monoxide²⁴. Never run a petrol or diesel generator indoors: they can produce fatal levels of carbon monoxide⁸.

Getting your heating checked by a qualified engineer

"Qualified" has a specific meaning for each trade, and it is worth knowing before you book.

For gas work, it means a Gas Safe registered engineer. Have your heating and cooking appliances checked by a Gas Safe registered engineer to make sure they are working safely²⁵. Contact a Gas Safe registered engineer to check your heating and cooking appliances are working properly and are safe²⁶. The same advice appears across NHS winter guidance: contact a Gas Safe registered engineer to make sure your heating and cooking appliances are working properly²⁷.

You can verify the person at your door. All Gas Safe registered engineers carry ID cards which tell you which appliances they are qualified to work on, and their competencies are clearly marked on the back of the card¹⁵. The Gas Safe Register's Check an Engineer service lets you input the licence number from the engineer's ID card to see pictures of the registered engineers and details of their qualifications¹⁵. Our guide to finding a Gas Safe registered engineer and checking their card walks through this.

For electrical work, it means a qualified electrician, as set out above. For the boiler itself, the check is a condition of switching it back on, not a service you can defer.

Carbon monoxide and gas smells after a flood

Two hazards deserve their own section because they can hurt you before the boiler is ever switched on.

Carbon monoxide is odourless and comes from fuel-burning appliances and equipment. Be aware of the signs of carbon monoxide poisoning and always ensure your property has a carbon monoxide detector⁸. Have your heating and cooking appliances checked by a Gas Safe registered engineer to help protect you from exposure to high levels of carbon monoxide²⁹. If an alarm activates or you suspect carbon monoxide, isolate all possible sources, ventilate the property and get out, then call a qualified engineer to check for a leak¹⁷. The fire and rescue service's TASK advice is to turn off or extinguish fuel-burning appliances if it is safe to do so, open doors and windows and go outside, seek medical assistance if unwell, and keep appliances off until checked by a qualified engineer¹⁷.

A gas smell is an emergency. In Northern Ireland, call the NI Gas Emergency Service immediately if you can smell gas⁶. Do not turn your gas supply on or use gas appliances until they have been checked by a Gas Safe registered engineer⁶. The same principle applies across the UK: leave the supply off and let the emergency service and a registered engineer take it from there.

If you need help while the heating is off

A cold home while checks are arranged is uncomfortable but manageable. The NHS advises that heating and cooking appliances are checked by a Gas Safe registered engineer so they are working safely²⁵, and that keeping warm matters for health in cold weather. If you have older neighbours, relatives or anyone with a health condition, check on them while their heating is off.

For wider help during a heating failure, our gas and heating failures section covers boiler breakdowns in cold weather, loss of supply and reconnection. If your boiler is a particular model, the fault code and breakdown pages for that model explain what the display is telling you, but none of them override the post-flood rule: the system is checked by a qualified person before it is switched on¹³.