What improves, on a system that needed it
Radiators heat fully and evenly
The most immediate and visible change. Panels that were cold across the bottom third heat all over, which means rooms that were never quite warm enough reach temperature.
The system heats up faster
Restored circulation means heat reaches the radiators sooner. On a badly restricted system this is a noticeable difference in how long the heating runs before the house feels warm.
The boiler stops kettling
Kettling is deposits on the heat exchanger causing localised boiling. Remove the deposits and the noise goes. This one matters beyond comfort — sustained kettling shortens a boiler's life.
Fewer component failures
Circulating abrasive particles wear pumps, diverter valves and thermostatic valve pins. Taking them out of the water extends the life of all of it.
The boiler warranty stays intact
If a new boiler is going in, a documented clean is what protects you when a heat exchanger fails and the manufacturer asks about system water quality. BS 7593:2019 sets out what that involves.
Some reduction in gas use
Real, but variable. A system that was running long cycles to heat cold rooms will use less gas once it is working properly. How much depends entirely on how bad it was. Anyone quoting you a specific percentage before seeing the system is guessing — including the previous version of this website, which advertised 25%.
What it will not fix
Being clear about this saves people money:
- Undersized radiators. If a radiator was never big enough for the room, a clean one still will not be.
- A failing boiler. A flush does not rejuvenate worn components or a failing PCB.
- Poor insulation. A warm house that loses heat quickly is a fabric problem.
- Bad balancing. Should be corrected as part of the job, but it is a separate issue from sludge.
- Air ingress. If air keeps getting in, something is drawing it in, and the flush does not address the cause.
- Limescale on its own. Needs a descaler in the mix, not just a flush.
- Existing leaks. And on very old systems, a flush can bring a weeping joint to light.
How long the benefit lasts
That depends entirely on the aftercare. A flushed system with the correct inhibitor dose, a magnetic filter emptied annually, and no fresh water being drawn in can go a very long time without needing it again. The same system with no inhibitor and no filter will be back where it started within five or six years.
The flush is the expensive part. The part that determines whether you have to buy it again costs under £250.
Common questions
Will a power flush reduce my heating bills?
On a system whose circulation was genuinely restricted, yes, because the boiler runs for less time to reach the same temperature. The size of the saving depends entirely on how bad the restriction was, and cannot be predicted before an engineer has seen the system. Treat any specific percentage quoted in advance with scepticism.
How long does a power flush last?
It depends on aftercare rather than the flush. With the correct inhibitor dose and a magnetic filter that is emptied annually, a system can go well beyond ten years. Without either, sludge typically returns within five to six.