Is no heating or hot water an emergency?

When your boiler stops and the house starts to cool, it's hard to know whether to ring an engineer straight away or wait for a normal appointment. No heating or hot water on its own is usually urgent rather than an emergency. It becomes an emergency if you can smell gas, there are signs of carbon monoxide, water is leaking from the boiler, or someone at home is at real risk from the cold.

This guide helps you work out which situation you're in, what to do in each, the few checks you can safely make first and how to keep warm while you wait. You can look at the controls and the pressure gauge yourself, but never remove the boiler's casing or touch any gas parts.

When gas or carbon monoxide makes it an emergency

If you smell gas, act straight away:

• Open doors and windows to let fresh air in.

• Turn off the gas at the meter, and turn off any gas appliances.

• Don't use light switches or anything electrical, don't smoke and don't use a naked flame.

• Call the National Gas Emergency Service on 0800 111 999. The line is free and open 24 hours.

Carbon monoxide (CO) is a poisonous gas you can't see. A boiler can produce it when it isn't burning its fuel properly. Warning signs include a CO alarm sounding, headaches, dizziness, feeling sick, tiredness or breathlessness that ease when you go outside, a lazy yellow or orange flame on a gas appliance, and dark sooty marks around it. If you suspect CO, stop using the appliance if it's safe to do so, get outside into fresh air and call 0800 111 999. Call NHS 111 for advice if anyone has symptoms, or 999 if someone is struggling to breathe or is confused.

When a leak makes it urgent

Water dripping from the boiler or the pipes underneath it needs dealing with quickly, because water and electrics don't mix. Switch the boiler off at its power switch, which is usually a fused switch on the wall nearby. If the leak is heavy, turn off the water at your main stop tap.

Look outside too. A short copper pipe coming through the wall from the boiler that is dripping or running means the pressure relief valve, a safety valve that lets water out when the pressure gets too high, has opened. Switch the boiler off and get it checked rather than topping it up and carrying on. For a leak that's spreading or coming through a ceiling, our emergency plumbing service is the right place to start.

When the cold itself makes it urgent

For most healthy adults, a night without heating is uncomfortable rather than dangerous, but not for everyone. The UK Health Security Agency advises people over 65, or with a long-term health condition, to heat the rooms they use most to at least 18°C if they can.

If you have a baby, an older relative or someone unwell at home, and it's cold outside, treat a breakdown as urgent and say so when you call. If you rent, tell your landlord straight away. Landlords are responsible by law for keeping the heating and hot water in repair.

Safe checks before you call

These checks only involve your controls and the outside of the boiler:

• Power: is the boiler's display lit? Check its switch is on and nothing has tripped at your consumer unit (fuse box).

• Controls: make sure the thermostat is set above the room temperature, the programmer is calling for heat, and any wireless thermostat has working batteries.

• Pressure: most sealed systems sit around 1 to 1.5 bar on the gauge when cold. Below that, the boiler may shut itself down.

• Gas supply: if your hob won't light either, the problem is the gas supply, not the boiler. On a prepayment meter, check you have credit.

If a fault code is showing, you can try one reset following the manual. Our guide on how to reset a boiler safely explains how and when to stop. If it locks out again, leave it off and arrange a repair.

If you heat with oil

If your home runs on oil rather than mains gas, there are a few extra things to check. First, look at the tank gauge. Running out of oil is a common cause of a sudden breakdown, especially at the start of the heating season.

After a delivery, don't keep pressing the reset button. Air can get into the fuel line when a tank runs dry, and repeated resets can push unburnt oil into the boiler. Give the oil time to settle as your supplier advises, try one reset, and if it doesn't fire, call an OFTEC registered engineer. OFTEC is the body that registers engineers who are qualified to work on oil heating. If you can smell oil fumes indoors, switch the boiler off, open windows and get it checked before using it again.

Keeping warm while you wait

A few simple steps make the wait easier:

• Choose one room to keep warm, close its door and spend most of your time there.

• Use a portable electric heater if you have one. Plug it straight into a wall socket, not an extension lead, and keep it clear of curtains and furniture.

• Never use a gas cooker, a camping stove or a barbecue to heat a room, as they can all give off carbon monoxide.

• For hot water, an electric shower works separately from the boiler, and a kettle will cover washing up.

What happens when an engineer visits

When you call, have the boiler's make and model to hand and a photo of any fault code on the display.

Our engineers are Gas Safe registered for gas boilers and OFTEC registered for oil. On a breakdown visit, they find the cause, make the boiler safe and explain the problem in plain terms before any work starts. Most faults can be repaired. If a boiler isn't worth repairing, we'll tell you honestly and talk you through the options, so you can decide what's right for your home.

If your heating or hot water has stopped and the checks above haven't helped, Pro Plumbers can help. Book a visit through our boiler repair service and let us know who's at home, so we understand how urgent it is.