What central heating leak sealer is sold to do
Central heating leak sealer is a liquid you add to the water inside your heating system. It is sold to travel round with the water, find small weeps and close them from the inside, so the system stops losing pressure without being emptied. What it cannot do is show you where the water was going, or what that water has already reached.
People usually buy a bottle when the boiler needs topping up more often than it should. Many boilers sit at around 1 to 1.5 bar on the gauge with the system cold, and your boiler manual gives the right figure for yours. If you are bringing it back up every few days, water is leaving the system somewhere, and adding sealer is aimed at that loss without anyone having seen where it is.
Why it does not tell you where the leak is
Sealer works blind. It circulates through the whole system, so nothing records where it acted, or whether it acted at all. If the pressure then holds for a while, you still do not know whether the leak was at a radiator valve, a joint under the floorboards or a pipe buried in a concrete floor, and each of those has a different repair.
That matters because heating water that escapes does not disappear. Under a solid floor it can soak into the screed, the layer of sand and cement laid over the concrete, and spread before anything shows. Under timber floors it can wet joists and the ceiling below. A leak that slows but does not stop can carry on like that out of sight, with the pressure gauge as the only clue.
Why we ask whether sealer has been added
When you ring about a heating leak, expect three questions: how often you refill the system, whether its pipes lie under timber boards or in concrete, and whether any sealant has gone into the system. That last question is there because sealant can stop testing working. Please mention it when you book and, if you know, roughly how long ago it went in and how much was used. A photo of the bottle helps.
Each of our tests depends on the leak still letting something out. Pressure testing watches for a fall on a gauge once a section is closed off. Tracer gas, a hydrogen and nitrogen mix, has to escape at the hole to be picked up at the surface. Thermal imaging looks for warm water spreading where it should not be. A hole that sealer has partly closed may let out too little to show, so readings can look quieter than the leak really is.
Signs the leak needs finding rather than sealing
Some signs suggest the escaping water is reaching the fabric of the house, or that the leak is more than a weep. When you see them, the useful next step is finding the point, so the repair can start in the right place before the damage spreads further. These are the signs to look out for:
The gauge needs bringing back up every few days, or sooner
The pressure kept falling after sealer went in
A warm patch on a tiled or concrete floor
A damp mark near a radiator pipe, or a stain on the ceiling below
An engineer has passed the boiler, yet the pressure still drops
Talk to your heating engineer first
Before you search for the best central heating leak sealer, ask a heating engineer to look at the boiler. Pressure can fall for reasons that have nothing to do with a leaking pipe: a pressure relief valve letting water out through the small pipe that runs from the boiler to an outside wall, for example, or an expansion vessel that has lost its charge. Neither of those is a leak in the pipework.
Ask the engineer, too, whether anything should go into your system at all. Boiler instructions may say what can and cannot be added to the heating water, and the engineer will know what is in there already. If you do go ahead, the product's own instructions explain how to use central heating leak sealer in your kind of system. Keep the bottle, so you can tell us what went in.
How a heating leak is found
Everything begins with the history: how often you refill, how far the pressure drops, where the pipes go and whether sealant is in the water. Before you book, the price is settled over the phone or by email. It pays for up to a half or full day's testing, and it does not drop if the leak shows itself early. Our no find, no fee on home water leaks does not cover central heating, so we say so at the start; full conditions are on our terms page.
On the day we close off parts of the system and pressure test them to narrow down where water is being lost. With the heating warm, thermal imaging picks out hot water spreading under a floor or behind a wall. A second method, such as tracer gas, has to agree with the first before the place is marked and photographed. The written report, made for a trace and access claim, is sent after full payment for the visit.
Mending the leaking pipe is usually something we can take on too, quoted separately. Repairs are guaranteed for 3 months, covering the pipework and fittings we install. If we give a repair price before we start, it only holds when the pipe is fixed on the day of the detection. If a floor has to be opened, the marked spot is the best place to start.