How much does it cost to replace a diverter valve in the UK?
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →Diverter valve replacement is inside a gas appliance and must be done by a Gas Safe registered engineer.
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Most likely cause & what to check
A diverter valve replacement on a combi boiler typically costs £150–£350 including parts and labour. The valve itself costs £30–£120 depending on the boiler brand; labour is 1–2 hours at engineer rates.
The diverter valve switches the boiler between heating mode (radiators) and hot water mode (taps and shower). When it fails or sticks, the common symptom is: heating works but no hot water, or hot water works but no heating.
Some engineers attempt to clean or free a sticking diverter valve before replacing it — this can cost £80–£150 for the call-out and is worth trying first if the valve is simply sticky rather than mechanically failed.
Parts availability varies significantly by boiler brand. Worcester Bosch and Vaillant parts are well-stocked and usually available same or next day. Budget brand parts can take several days to source, meaning you are without hot water in the meantime.
If the diverter valve replacement does not fix the problem, the next suspects are the thermistor (NTC sensor), plate heat exchanger, or the PCB. Ask the engineer to diagnose thoroughly before quoting for additional parts.
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