BoilerFaultCodesBoiler leaking water? Do these three things now.
A leaking boiler is water meeting electricity, so this is one of the few faults where you act before you understand it. Sort the immediate risk, then work out what has gone wrong.
- 1 Turn the boiler off Use the switch or the programmer. If water is anywhere near the electrics, switch it off at the fuse spur instead.
- 2 Turn off the water to the boiler There is usually an isolation valve on the pipework underneath. If you cannot find it, use the main stopcock.
- 3 Catch the water and turn the heating off A bowl and towels. Then leave it off until someone has looked at it, because running a leaking boiler makes things worse.
Do not try to fix a boiler leak yourself. Everything inside the casing is sealed, pressurised and next to live electrics, so it is Gas Safe engineer work by law and by common sense. What follows is so you know what you are being told and what it should cost.
Where is the water coming from?
The location narrows it down more than anything else. Have a careful look before you ring anyone, because it changes the answer and the price.
From a pipe on an outside wall
£0 to £180Likely: The pressure relief valve discharging
A sealed system has a relief valve that dumps water outside if pressure gets too high. Water from that copper pipe is not really a leak, it is the safety device doing its job. Check the boiler gauge: if it is up near 3 bar, bring the pressure down and it may stop. Valves often fail to reseat afterwards and keep weeping, in which case the valve needs replacing.
How to lower boiler pressure →From underneath, clear water, worse when heating is on
£120 to £350Likely: A failed pump seal or a pipe joint
Pump seals wear out and weep, usually more when the system is hot and running. Compression joints on the pipework under the boiler can also loosen over time. Both are routine repairs.
From inside the casing, and the pressure keeps dropping
£400 to £900Likely: The heat exchanger
This is the expensive one. A corroded or cracked heat exchanger leaks internally and the system loses pressure constantly. On an older boiler the part plus labour often approaches the price of a replacement, so get a quote for both before deciding.
Repair or replace? →A slow drip from the top of the boiler
£90 to £180Likely: The automatic air vent
The auto air vent releases trapped air. When the seal perishes it lets water past as well. Small job, cheap part.
Milky or slightly acidic water near the base
£80 to £200Likely: The condensate pipe or trap
Condensing boilers produce acidic condensate. If the trap cracks or the pipe comes loose, that water ends up on the floor. It can stain and it should not be left.
Only right after someone topped up the pressure
£0 to £120Likely: The filling loop
Filling loops are often left slightly open or not disconnected properly. Check both valves are fully shut. If the loop itself is passing water, it needs replacing.
Costs are typical UK ranges including parts and labour. A diagnostic callout is often £60 to £100 and is usually credited against the repair if you go ahead.
Losing pressure but no visible water?
A system that keeps dropping below 1 bar with nothing on the floor is still leaking somewhere. Pipework under floors, behind walls or a slow internal weep will do it. The pressure gauge is the evidence even when the puddle is not.
Why boilers lose pressure →Is it covered?
Worth checking before you pay for anything. Boiler cover and home emergency policies usually treat a leak as an emergency callout. If the boiler is under manufacturer warranty, a heat exchanger failure should be covered outright, though most warranties require proof of annual servicing, so dig out the paperwork before you ring.
Water damage to floors and ceilings normally falls under buildings insurance rather than boiler cover. Photograph everything before you mop up.
When it is urgent
Call someone straight away if water is running onto electrics, if you can see scorching or smell burning, or if the leak is heavy enough to be damaging the building. If you smell gas at any point, leave the house and ring the National Gas Emergency line on 0800 111 999.
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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