The house is older than its heating by about seventy years
An Ealing Edwardian semi or terrace was built with fireplaces, not radiators. Central heating arrived somewhere between the 1960s and the 1990s, and it was installed into a finished house by running pipework wherever there was a route. In these properties that route is nearly always the same: up from the boiler, under the suspended timber ground floor, and through the joists.
That matters because it tells you where to look. You are not hunting a designed installation with a drawing. You are hunting somebody's practical solution to getting a pipe from A to B in an afternoon, and the failures are at the points where that solution was compromised.
Microbore, and where it fails
A great many of these retro-fits used microbore: 8mm or 10mm soft copper run in long continuous lengths from a central manifold to each radiator. It was quick to install, it snaked through joists without fittings, and it used far less copper than a conventional two-pipe system.
Its weaknesses are specific rather than general:
- The fittings at each end. The pipe itself, being continuous, rarely fails mid-run. The compression joints at the manifold and at the radiator tails do, particularly where the soft copper was over-tightened or where the pipe was not fully square into the fitting.
- Kinks. Soft copper bent too tightly during installation thins on the outside of the bend. Those points fail years later.
- Blockage and sludge. An 8mm bore silts up far faster than a 15mm one. That gives cold radiators rather than leaks, but a blocked circuit raises pressure elsewhere.
- Contact corrosion. Copper in direct contact with a steel nail plate, a screw or damp timber pits from the outside.
If one radiator has been slow or cold for years and the system now loses pressure, those two facts are related more often than not.
Notches, and the nail that went through
To get a pipe across joists, the installer either drilled through them or notched the tops. Both were common; neither was always done to the depths and positions that the structure would want.
Two failure modes follow. The first is mechanical: a pipe sitting in a shallow notch directly beneath floorboards is within reach of a floorboard nail or a later screw. A punctured pipe under a board can weep for years, and the trigger event is often remembered, because the leak appeared shortly after a carpet was fitted or a floor was screwed down.
The second is thermal. A pipe in tight contact with timber, or clipped rigidly at both ends of a long run, cannot expand freely. It creaks when the heating comes on, which everybody in these houses recognises, and the strain goes into the joints.
If you have a heating leak and a memory of somebody putting screws into the floor, start there. It is the highest-yield question on this entire page.
The advantage you actually have
Everything above is bad news. Here is the good news, and it is substantial: a suspended timber floor comes up.
Compared with a screed floor, a concrete slab, a mansion block or a tower, an Edwardian ground floor is the easiest structure in London to investigate. Boards lift on their joints, the void beneath is often deep enough to crawl or at least to see along with a torch and an inspection camera, and the pipe run can frequently be followed visually from one end of the house to the other without cutting anything at all.
Which means the detection strategy here is different. Thermal imaging is used to choose which board to lift rather than to avoid lifting one. On many of these jobs the right sequence is: confirm the loss, isolate the circuit, lift three boards at the most likely point, and look. That is faster and cheaper than an elaborate non-invasive survey, and we will say so rather than sell you equipment time you do not need.
The exception is the hall and any room with original encaustic or quarry tiles on a solid base, and any room where the boards have been replaced with chipboard or engineered flooring glued down. There, the non-invasive route earns its keep.
The test to do before anyone attends
Note the boiler pressure cold, then leave the heating off entirely for twenty-four hours and read it again. Then run the heating normally for a day and read it again. The pattern separates three quite different problems:
| Pattern | What it means |
|---|
| Falls with the heating off | A real leak, losing under static pressure. It is somewhere in the pipework or the boiler. |
| Holds when off, falls only when running | A leak on a circuit that only pressurises with the pump running, or a failed expansion vessel. |
| Climbs high when hot, falls below normal when cold, no water anywhere | Almost always an expansion vessel that has lost its charge. Not a leak at all, and not a floor to lift. |
That twenty-four hours of observation is worth more than the first hour of any engineer's visit. Our boiler pressure pages go through it in more detail, and pressure dropping with no visible leak covers the case where nothing shows.
The cost nobody mentions: refilling an old system
When an old system is drained to repair a leak and then refilled with fresh oxygenated mains water, two things follow that are worth budgeting for.
First, the fresh water accelerates internal corrosion unless the inhibitor is replaced. On a system that has been running for thirty years with whatever inhibitor is left in it, a drain-down is the moment to put that right, and it is cheap at that point and expensive later.
Second, disturbing an old system dislodges sludge, and sludge that was sitting harmlessly in the bottom of a radiator ends up in a pump, a valve or the boiler's heat exchanger. On a heavily silted microbore system it is not unusual for a repair to be followed by a cold radiator that was fine the week before. That is not the repair going wrong; it is an old system being moved. A power flush or at least a magnetic filter is the sensible companion purchase.
We will say this before the work rather than after. Radiator and valve leak repair covers the visible end of the same system, and a radiator leaking from a valve is where to start if the water is appearing at a radiator rather than under the floor.
