A power flush looks simple from the outside — a machine, some hoses, a lot of dirty water. But a good flush is a methodical process. Here’s what happens, step by step.
The equipment
A power flushing machine is essentially a powerful, portable pump with a tank, a flow-reversal valve and a dump valve. It’s connected into the heating circuit so that it replaces your system’s own pump for the duration of the flush. Compared with a domestic circulating pump, it moves much more water — but at low pressure, so it isn’t forcing the system beyond its normal limits.
Alongside the machine, engineers use cleaning chemicals, a radiator vibrating tool, and a way of testing water quality — often a conductivity (TDS) meter.
assets/img/photos/power-flushing-equipment-chemicals.webpWhat happens during a power flush
System check
The engineer checks the boiler, radiators, valves and pipework, notes any weeping joints or seized valves, and tests the water. This decides whether a power flush is suitable.
Connection
The circulating pump is usually removed and the machine connected in its place using adaptors. Alternatively, it can be connected across the flow and return near the boiler, or at a radiator. On open-vented systems, the feed and vent are isolated.
Chemical circulation
A sludge remover is added and circulated through the whole system, warm where possible, to soften and loosen deposits. A descaler may be used if there’s limescale.
Radiator-by-radiator flushing
All radiators are closed except one. The machine’s full flow goes through that single radiator, with the direction reversed repeatedly. The radiator is agitated to shake loose settled sludge. Then the next radiator is opened and the last one closed.
Dumping to waste
Once deposits are mobile, the dump valve sends dirty water to drain while clean mains water is fed in. Each radiator is dumped in turn until its water runs clear.
Testing
Water quality is checked against the incoming mains supply. When the readings are close, the system is clean.
Inhibitor and recommissioning
The pump is refitted, the system refilled and bled, and inhibitor added at the correct concentration. The boiler is fired and each radiator checked for even heat.
Why radiator-by-radiator is essential
Water takes the path of least resistance. If every radiator is open at once, the most blocked radiators — the ones that need cleaning most — receive the least flow. Isolating radiators one at a time forces the full flow through each in turn. That’s the single biggest difference between a thorough power flush and a quick one.
What about the boiler?
The water passing through the boiler is cleaned along with the rest of the system. On some systems, engineers will isolate or bypass the boiler for parts of the flush to avoid pushing heavy debris through it. See can power flushing damage a boiler?
Learn more
For timings, see how long does a power flush take? For our service, see power flushing in London.