Is this a faulty shower cartridge?

[diy_fun_uk]

Shower works off combi. Hot water e.g. from kitchen/bathroom sink appears to be working ok, not going cold. However when show is run, it intermittently goes cold then heats up again.

Rather than a faulty combi boiler, is this more likely to be a faulty shower?

 

[m0t]

Is your cold feed coming from a loft tank?

When I had my shower connected to a loft tank and a combi the combi would run for 10s then switch off for 10.

The mismatched pressures from the shower caused not enough hot to be called for so the boiler wasn't detecting the need for heat.

Fixed by running a mains feed

 

[Jackrae]

The rate of hot water demand from the shower valve is probably too low for the boiler to operate correctly. This is probably due to a boiler control problem, but to get around it (inefficiently) try running the basin hot tap at a low rate just sufficient to maintain a steady flow of hot water - you may then find the shower performs OK whilst the tap is left running.

 

[picasso]

Or try fitting a bigger shower head.

 

[diy_fun_uk]

thanks guys, reason I wondered if it was a faulty cartridge or something else 'in' the shower is it's worked okay for over a year. I rent the place out, first tenants in for 12 months, no issues, most recent tenant in for around 4 months and just started playing up recently.

 

[Jackrae]

Or a boiler fault (at the lower flow that a shower takes compared to a basin tap)