Shower cartridge changed but still intermittent temp

27 Sep 2007
Reaction score
United Kingdom
Was convinced the 15 yr old cartridge needed replacing to sort our shower temp problem.

But it seems the worcester 28cdi is cutting in and out,

whats the cure please ?

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Is it just the shower or also the taps at basin and sink that there is an issue.
I would first check that the water pressure at the boiler is adequate, as this can affect the hot water supply.
The hot water to basins are fine,
pressure throughout is good, even when shower goes hot / cold pressure remains the same, which is confusing.

burner light goes on off, is it somethink to do with the big red vessel inside, which holds or balances the hot water ?

thanks for any constructive comments
More likely to be a flowrate issue - insufficient flow causes the boiler to cycle or possible scaling of the heat exchanger.

If you take the shower head off and run the shower does the boiler still cycle?

The pressure vessel is not related to hot water supply & the pressure gauge is showing the pressure in the heating circuit - not related to your hot water/cold water pressure
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Remember although the shower may feel like a lot of waters comming through, its less than you think, and a mix of the two supplys. So running a HW tap is not a fair comparison.

Run a HW tap but slow it down quite a bit (not to a treakle, but maybe half way) and see if the boiler custs in and out, and more importantly if that is noticable at the tap.

If it is various issues could cause the boiler to do this. Most with Scale/Dirt, but some with Gas Regulation and electronics so do as above and if it is struggling keeping steady heat at the taps on mid/low flow, then its time to gall an RGI to look at the boiler
Fit an electric one. :LOL: What make is it and when was it installed?
Took the shower head off, then dismantled, surprised how many parts inside, anyway got it back together. It was all spotless, even the mesh filters :LOL:

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