Aqualisa Replacement Cartridge Urgent Help Required

22 Aug 2008
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United Kingdom
Hi everyone, had to replace the valve on the shower in my son’s house today. I’ve done it before on my own house and wasn’t expecting any issues.

His heating system is a Potterton with a boiler with a pressure tank. I turned the water off at the mains, but also at the tap adjacent to the boiler.

After fitting the new cartridge I turned the cold back on and then the hot, however things didn’t go as expected. When the hot is switched on at the boiler the hot water comes out of the shower regardless as to whether the shower is switched off or on, and is merely slightly cooler if in the off position, but is also coming out at much higher pressure if the shower tap is in the off position. I took the replacement one out and tried the old one again but with no difference. Did I do anything to the hot water boiler system by switching off after the boiler?

I don’t know what to do now? I can’t see any obvious reason why the shower is behaving as it is. I have made sure that channel in the cartridge matches with the channel in the housing, i.e. both are in the 3 o'clock position.

Unfortunately the only way to get the shower off is to switch the tap by the boiler.
Last edited:
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Did you fit the new hot water seal in the back of the shower
Hi Steve

Thanks for that.

Took it apart again and indeed the washer had come adrift. We re-seated it and put it all back together and it is working fine, except that you need to turn the knob anti-clockwise to turn it on and vice versa to off, which seems to me to be counter-intuitive. Is it?

But thanks for the tip, it's much appreciated.
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I'm sorry to that the problem with the hot water coming through when the shower is off is happening again. In fact the shower came on of its own accord during the night. We've tried taking it out and replacing it again but it without success. The hot water is running regardless as to whether the shower is on or off.

Any ideas anyone?
The cartridge is £100

I had an aqua Lisa which had a leaking cartridge. It is cheaper to just replace the whole thermo valve then replace cartridge

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