Power shower cuts out

[chilscout]

My power shower pump serves two showers. One works fine but the other keeps cutting out for a few seconds, restarting then cutting out again.

I've checked the pipework, hose and showerhead and they seem fine, so only thing I can think of is the mixer. It's an old Grohe Grohtherm 100 concealed.

Is it likely to be the thermostatic valve or the flow control? How do I test?

 

[jj4091]

Are you sure you got the model number correct https://www.google.com/search?q=Gro...gBAZgCAaACdpgDAJIHAzAuMaAH7gQ&sclient=gws-wiz seems to thermostatic.

 

[chilscout]

Sorry, should have read Grohtherm 1000. Model number is 19236.

One thing I do notice is that when the flow stops, if I drop the showerhead below the valve height, it 'seems' to work okay.

 

[trojanhawrs]

How high is your cold water tank above the shower?

 

[chilscout]

Around 4-5ft above showerhead. The shower has been working fine for years

 

[trojanhawrs]

Something's causing a flow restriction anyway, I'd imagine the flow control is just a manual valve so unlikely to cause intermittent issues like that. Probably worth taking a look at the filters/cartridge