What a diverter valve does, and how it fails
The diverter valve switches heated water between the central heating circuit and the hot taps every time someone asks for hot water. It cycles constantly, which is why it is one of the most common parts on a combi boiler to wear out, through a seized mechanism, a perished diaphragm or a failed actuator.
The usual symptoms are hot water that runs only lukewarm, radiators warming up when only hot water has been drawn, or hot water available solely while the heating is on.
Which part you need
Not every fault needs a whole valve. Which format applies depends on the brand:
- Complete assemblies, where the valve body itself has failed. Ideal 176550 and Vaillant 0020132683 are typical.
- Cartridges and repair kits, where the internal mechanism can be swapped without the body, such as the Ideal 175668 cartridge.
- Diaphragms and seal kits, the rubber parts that perish and let water bypass internally, such as the Baxi 5111137 repair kit.
- Motors and actuators, for motorised valves where the electrics have stopped switching but the body is sound, such as the Glow-worm 20118640 and Worcester 87161087230.
- Retaining clips and fixings, easily lost or damaged during the change.
Finding the right one
Start with the boiler's model name and GC (Gas Council) number, on the label behind or beneath the front casing. Designs vary between manufacturers and often between revisions of the same boiler, and several ranges switched from a mechanical, pressure-operated valve to a motorised one mid-generation, so matching on model alone can return the wrong part. Where you can, cross-check the number stamped on the old valve. Our guide to identifying the right boiler spare part goes through it in full, or the parts finder searches by brand and model.
Common questions
Can I replace just the cartridge, or do I need the whole assembly? It depends on the brand. Some boilers take an internal cartridge or a seal and diaphragm kit; others need the complete valve. Check before ordering, as fitting the wrong format is the most common cause of returns.
Are these genuine parts? Yes. Our diverter valve spares are genuine manufacturer parts, not aftermarket substitutes.
Still not sure? Call the team on 01934 253600 and we can usually identify the valve from the boiler's data badge. For other faults, see gas boiler parts or the full spares and accessories range.
