Thermostatic shower running too hot or too cold
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →Thermostatic showers are brilliant at maintaining a steady temperature, but when they start playing up, it's genuinely frustrating. You'll turn the dial expecting a pleasant warm shower and get blasted with either scalding water or an uncomfortably cold trickle instead. This usually happens because something's shifted in your home's water system — perhaps a new boiler's been installed, water pressure's changed, or someone's fiddled with the temperature settings. The good news is that many of these issues are straightforward to sort out yourself, though occasionally the cartridge inside the valve simply wears out and needs replacing by a qualified plumber.
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Most likely cause & what to check
Check whether anything has changed recently — a new boiler, altered water pressure, or someone adjusting the temperature limiter are common causes.
Look at the shower dial — some thermostatic valves have a small cover cap that hides a temperature limit screw. Try removing the cap and adjusting the temperature limit slightly.
If the temperature is erratic or won't stabilise at all, the thermostatic cartridge inside the valve has failed. Call a plumber. Tell them: "My thermostatic shower is running too [hot/cold] and the dial doesn't seem to make a difference."
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Frequently asked questions
Why does my thermostatic shower suddenly run too hot when someone uses another tap?
This is classic thermostatic valve behaviour when water pressure drops suddenly elsewhere in the home. The valve struggles to balance the hot and cold supplies, so you'll feel a temperature spike. It usually settles within a few seconds, but if it's severe or persistent, you may have a pressure issue that a plumber should investigate.
Can I adjust the temperature limiter myself without calling a plumber?
Yes, you can have a go at adjusting the limit screw if your valve has one — it's usually hidden under a small cap on the dial. Turn it very slightly (quarter turns only) and test the water before making another adjustment. If you're not confident or it doesn't improve things, stop and ring a plumber rather than risk damaging the valve.
How do I know if my thermostatic cartridge has actually failed?
The main tell-tale sign is that the dial becomes unresponsive — you'll turn it but the water temperature won't change at all, or it'll swing wildly between hot and cold without stabilising. If adjusting the temperature limiter doesn't help and the problem's been ongoing for weeks, the cartridge has almost certainly failed and needs replacing.
Does a new boiler installation affect my thermostatic shower?
Yes, absolutely — changing your boiler can alter the water pressure and temperature delivery to your shower. If you've just had a new system fitted and your shower's started playing up, mention this to your installer or plumber, as they may need to recalibrate the thermostatic valve or adjust your system settings.
What's the difference between a thermostatic valve failing and water pressure problems?
With a failing valve, the dial won't respond or responds very sluggishly to your adjustments. With pressure problems, the dial usually works fine but you'll notice temperature changes when other taps or appliances run elsewhere in the house. A plumber can test your water pressure quickly to rule this out.