Boiler replacement, servicing and heating repairs

A combi boiler heats water on demand straight from the mains, so there is no hot water cylinder and no tank in the loft. It suits flats and smaller houses with one bathroom, but it depends on decent mains pressure and flow, and running two showers at once is where it struggles.

A system boiler heats a stored cylinder, usually an unvented one fed at mains pressure. It is the usual choice for homes with two or more bathrooms. A regular or heat-only boiler works with a cylinder and a cold water tank in the loft; it is common in older houses and can make sense where the pipework was designed around gravity-fed hot water.

Replacing like with like is normally the simplest job and usually costs least. Switching type, for example taking out a cylinder and tanks to fit a combi, means pipework changes and sometimes a larger gas supply pipe. A good engineer asks how many people live in the house and how you use hot water before recommending either.

Anyone paid to work on gas appliances in a home must be Gas Safe registered and competent for that type of work. That includes LPG as well as mains gas. The categories an engineer is qualified for are printed on the back of their Gas Safe ID card, and you can check the registration on the Gas Safe Register website before anyone starts.

Oil boilers are not covered by Gas Safe. Look for a technician registered with OFTEC, the competent person scheme for oil heating. Oil tanks have their own rules under Approved Document J, which deal with fire risk and pollution, so a replacement tank cannot always go where the old one stood.

Fitting a new boiler needs Building Regulations approval. In practice a registered installer self-certifies the work: they fill in a commissioning record such as the Benchmark checklist and notify Building Control through their scheme, and the council later sends you a completion certificate. If a firm is not in a competent person scheme, the council has to be told before the work starts and a fee is payable. Keep the certificate; a buyer's solicitor will ask for it when you sell.

The Health and Safety Executive advises that gas appliances, flues and pipework are serviced at least once a year by a Gas Safe registered engineer, and most boiler warranties set conditions on servicing too. A service is not just a clean: the engineer checks combustion, the flue, the seals and the safety devices.

If an engineer finds a dangerous or at-risk installation, they will label it 'Danger Do Not Use' and may disconnect it. It is illegal to use a gas appliance you suspect is unsafe. If you smell gas, call the gas emergency number, 0800 111 999. Do not open up a boiler or try to reset internal parts yourself; beyond the controls on the front panel, the work belongs to a registered engineer.

Common repair calls are a frozen condensate pipe in cold weather, low system pressure, a failed pump or diverter valve and sludge in older systems. When you describe the fault, include the boiler make, model and any error code shown on the display. It helps the engineer bring the right parts.

Under the Gas Safety (Installation and Use) Regulations 1998, landlords must have every gas appliance and flue they provide checked every 12 months by a Gas Safe engineer. The record is often called a CP12 or landlord gas safety certificate. Existing tenants must receive a copy within 28 days of the check, and new tenants before they move in. Records must be kept for at least two years.

A check can be done up to two months before it is due while keeping the original anniversary date, but then you must keep the records until two further checks have been done. The annual check does not cover the installation pipework, so HSE recommends asking the engineer to test the whole system for tightness at the same visit. If a letting agent's contract makes them responsible, the same duties apply to the agent.

Source: hse.gov.uk

• the make, model and output of the boiler, and why that output suits your home
• the boiler type, and what happens to any existing cylinder or loft tanks
• the flue route and terminal position, and the condensate pipe route
• system cleaning or a power flush, and whether a magnetic filter is fitted
• the controls: thermostat, programmer, radiator valves and any smart or weather-compensating control
• any gas pipe upgrade from the meter
• Building Regulations notification, the commissioning record and who registers the warranty
• the warranty length and the servicing conditions attached to it
• removal and disposal of the old boiler

The Future Homes and Buildings Standards are changing the Building Regulations in England so that new homes are built with low carbon heating and on-site renewable electricity. They apply to new buildings; they do not require you to take out a working boiler in an existing home.

If you want to move off fossil fuel now, the Boiler Upgrade Scheme in England and Wales pays towards a heat pump or, for rural homes off the gas grid, a biomass boiler with an emissions certificate. The grant is not available for hybrid systems where a gas or oil boiler stays in. Pellet boilers need a dry fuel store, a suitable flue and regular ash removal, so they are a rural choice rather than a town one. In Scotland, Home Energy Scotland funds heat pumps and, where a heat pump is not suitable, some biomass boilers. In Wales, Nest can pay for heating improvements for eligible households, sometimes including a boiler repair or replacement. ECO4, funded by energy suppliers for low-income and vulnerable households, is due to close at the end of this year.

Solar thermal panels can pre-heat a hot water cylinder and pair well with a system or regular boiler. They do not suit a combi without a cylinder.

Describe your heating, the boiler's age and what you need, then confirm your mobile number with a text-message code and your email address with a link. We show the job, without your name or contact details, to heating engineers who cover your postcode. The first one to buy it gets it, and nobody else can: it is then taken off the shop. The engineer pays Offrano; you pay nothing to us.

Before the engineer sees your details, we email you their business name, address and phone number, and you can withdraw your consent at any time from a link in every email. We cannot promise that someone will take the job; if nobody does within 21 days, it is withdrawn. We check that buyers are registered businesses but not the quality of their work, so check the Gas Safe or OFTEC registration yourself.