Heating repair: boiler faults, cold radiators and no hot water

If you smell gas or suspect carbon monoxide, call the National Gas Emergency Service on 0800 111 999, stop using the appliance and open windows. The emergency service makes the situation safe; it does not repair your boiler, so you will still need an engineer afterwards.

Anything beyond the controls on the front of the boiler, the thermostat and the pressure gauge belongs to a qualified engineer. Taking the cover off a gas boiler is not a DIY job, and neither is work on an unvented hot water cylinder, which has safety valves designed to stop it failing dangerously.

Engineers can often narrow a fault down from a good description and bring the right parts. Note whether you have no heating, no hot water or neither; whether the boiler shows an error code or a flashing light; what the pressure gauge reads; and whether the problem started after a cold night, a power cut or other work in the house.

Common causes the engineer will consider: a frozen condensate pipe in cold weather, low system pressure from a leak or a failing expansion vessel, a stuck diverter valve on a combi when heating works but hot water does not, a failed pump, faulty thermostat or wiring, and sludge blocking radiators in older systems. Radiators cold at the bottom point to sludge; cold at the top, to air.

• boiler make, model and approximate age
• error code and pressure reading
• which of heating, hot water or both has failed
• type of hot water: combi, vented or unvented cylinder
• fuel: mains gas, LPG, oil or electric
• whether it is a rented home, and who the landlord or agent is

Any repair to a gas boiler or gas pipework must be done by a Gas Safe registered engineer qualified for that appliance type; the categories are on the back of their ID card. Oil boilers need an OFTEC-registered or similarly qualified technician. Work on an unvented hot water cylinder calls for specific training: Approved Document G points to registration with a competent person scheme for that work or a current registered operative skills card for unvented systems.

Building Regulations do not require advance approval for emergency repairs to a boiler or heating system, but the work must still follow the rules. If a repair turns into a boiler replacement, the replacement is notifiable and should come with the usual certificate.

A single failed part on a boiler that is otherwise in good condition is usually worth repairing. The balance shifts when parts are no longer available, the heat exchanger has failed, the boiler has needed several call-outs in a short time, or the engineer has classed it as at risk or immediately dangerous. Ask the engineer to put the diagnosis, the part and its cost in writing, and to say what else is worn.

If replacement becomes likely, it is a chance to consider whether a like-for-like boiler is still the right choice, or whether a heat pump would suit the house. In Wales, the Nest scheme can in some cases fund a boiler repair or replacement for eligible households.

Describe the fault and the system. Heating engineers in your area see it without your name or contact details, and only one of them can buy it. They pay Offrano for it; the service is free to you.

We email you the engineer's business name, address and phone number before your details are released. We cannot promise how quickly, or whether, someone takes the job, so for an urgent breakdown in winter you may also want to call engineers directly. Offrano does not check workmanship or Gas Safe status, so check the register yourself before anyone starts.