Plate Heat Exchangers in Combi Boilers
The plate heat exchanger is what actually heats your tap water in a combi boiler, transferring heat from the primary heating circuit through a stack of thin metal plates without the two water flows mixing.
The plate heat exchanger is what actually heats your tap water in a combi boiler, transferring heat from the primary heating circuit through a stack of thin metal plates without the two water flows mixing. It's a common point of scale build-up in hard water areas.
What it does
Corrugated plates create narrow channels that force heating water and mains water past each other in opposite directions, transferring heat rapidly through the thin metal walls.
How it fails
Limescale narrows the tap-water channels first, since that's the harder water passing through. Flow drops and the hot tap runs erratically hot and cold.
Repair or replace
A scaled exchanger can sometimes be chemically descaled if caught early. Once flow is badly restricted or plates are damaged, replacement is more reliable than repeated descaling.
Questions we get asked
Does swapping a plate exchanger have to be done by a Gas Safe engineer?
Yes, it's an internal boiler component and any work on it is carried out by a Gas Safe registered engineer.
Does a water softener prevent this?
It reduces scale formation significantly in hard water areas, though descaling and inspection are still worthwhile over the boiler's life.
How is this different from the main heat exchanger?
The main heat exchanger transfers heat from the burner into the heating circuit; the plate exchanger then transfers some of that heat again into your tap water.