Leaking Boiler Repair Cost: What Each Fix Typically Costs

Why the price depends on where the leak is

A leaking boiler is not one fault. It is water escaping from one of a dozen places, and each has its own part price and its own amount of labour. A joint under the boiler can be remade in under an hour with a few pounds of fittings. A heat exchanger means draining the system, stripping the boiler down and fitting a part that can cost more than everything else combined.

So the honest answer to “how much” is that nobody can price it properly until they know the source. A fixed figure quoted over the phone for an unknown leak is either padded to cover the worst case or likely to change on the day. The first thing that happens on a visit is finding the leak. If you want to narrow it down yourself before anyone arrives, which boiler pipe is leaking walks through the checks.

Typical costs by the part that is leaking

These are typical UK market ranges including parts and labour. London usually sits toward the top of each range because labour and parking cost more here. They are a guide to what the market charges, not our prices.

• Loose compression joint or weeping isolating valve under the boiler: roughly £100 to £250.
• Condensate pipe joint, section or trap: roughly £80 to £200.
• Pressure relief valve: roughly £90 to £200, depending on the make and whether the valve is easy to reach.
• Automatic air vent on the pump or heat exchanger: roughly £100 to £200.
• Expansion vessel recharge or replacement (often the reason the relief valve keeps dumping water): roughly £80 to £150 for a recharge, and £200 to £400 or more to replace a vessel, especially if it sits behind the boiler and the boiler has to come off the wall.
• Pump seal or complete pump: roughly £200 to £400.
• Diverter valve or internal seals on a combi: roughly £150 to £350.
• Heat exchanger: roughly £400 to £1,200 or more, and the part alone can be the bulk of that.

Anything inside the boiler casing is gas work. Gas work is carried out by Gas Safe registered engineers. A cheap quote from someone who is not on the Gas Safe Register is not a saving.

What changes the final bill

Three things move a repair up or down within those ranges.

The make and age of the boiler. Common parts for popular models are usually available from a merchant the same day. Older or less common boilers may need a part ordered, which can mean a second visit. Genuine manufacturer parts cost more than generic ones, but for valves and seals inside the boiler they are what the manual specifies.

Whether the system needs draining. Some repairs can be done by isolating the boiler. Others need the heating drained down, refilled, bled and repressurised, which adds time. If the system is full of sludge, the engineer may advise cleaning it before fitting an expensive new part, because dirty water is often what killed the old one.

When you call. Night and weekend work costs more with many firms. Ours is simpler: the £60 call-out is the same at any hour, and the repair price is agreed with you on site before any work starts. Our pricing page has the details.

Repair or replace a leaking boiler?

For most leaks, repair wins easily. A relief valve, a pump or a set of seals costs a fraction of a new boiler, and the rest of the appliance is often in good order.

The picture changes with a leaking heat exchanger on an older boiler. As a rough rule the trade uses, if a boiler is past about 12 to 15 years old and the repair costs more than half of a replacement, replacement is worth pricing. Parts for older models also get harder to find, and a boiler that has leaked from its heat exchanger may have other components near the end of their life.

A good engineer will tell you which side of that line you are on without pushing a new boiler. Repair or replace a broken boiler goes through the decision in more detail.

Check this before you pay anyone

Warranty. Many new boilers come with a manufacturer warranty of several years, often conditional on an annual service. If your boiler is still covered, call the manufacturer first. A repair by anyone else may void the warranty, and the manufacturer’s own engineer may fix it free.

Home emergency or boiler cover. If you pay for cover through your energy supplier or insurer, check what it includes and the excess before calling a private engineer.

Renting. Under section 11 of the Landlord and Tenant Act 1985, a landlord must keep the installations for space heating and heating water in repair. If you rent, report the leak to your landlord or agent in writing straight away. How long a landlord has to fix a boiler explains the timescales.

Stop the damage first. A leak left running can cost more in ceilings and flooring than the boiler repair itself. Switch the boiler off at the fused spur if it is dry, catch the water, and if it is heavy, turn off the stopcock.

How our leaking boiler repairs are priced

We keep it plain. The £60 call-out covers getting an engineer to you, day or night, anywhere in London and inside the M25. On arrival the engineer finds the leak, makes it safe and tells you what has failed. The repair price is agreed with you on site before any work starts.

If the part is to hand, the leak can be fixed on the same visit. If it has to be ordered, the boiler is left safe, isolated if need be, and the repair is booked in. See leaking boiler repair for what the visit covers, or emergency boiler repair if the leak has left you without heating or hot water tonight.