Grohtherm Wireless Pumped Shower Temperature Problem

Am hoping one of you experts (or DIY'ers!) can (please!) help with following: -

Installed Grohtherm Wireless pumped shower 18 months ago next to gravity fed HWS cylinder heated by off-peak immersion. All working fine until last week.

Returned from week away to find HWS immersion thermometer safety cut-out had tripped which meant that tank was now luke warm. Reset this (cause was wife hanging towels off HWS tank which covered the immersion ) and HWS reheated fine.

However, after HWS tank was back to normal temperature shower struggled to reach the standard 38C - I measured temp of water from HWS and it was 52C so ok and well within unit limits.

I than ran Inlet Valve cleaning procedure and after this the shower worked fine again - for 3 days. This morning had same problem - not reaching temperature.

If anyone has seen this before and knows of likely problem/fix that would be appreciated!

I haven't yet tried uncoupling the unit and cleaning inbound valves/filters (partly because there is no way of isolating inbound hot water as gate valve fitted to hot water feed is broken ) so I need to wait for weekend when I have some time. I did wonder if cartridge could be failing - but that wouldn't explain why it has worked for 3 days again?

Pressure/flow etc from shower is fine no obvious change from before.

I can get shower a bit warmer by increasing dial to say 42C but even when doing that the output water temperature is around 30C mark.

Thanks for your help.

I'd definately try cleaning the filters first. Try bunging the cold feed to the cylinder where it exits the cold water storage. A large lump of blu-tac will do the trick. Should allow you to replace the gate valve too.

Thanks for taking the time to reply Elkato531.

Yes will give that a bash. The gate valves* feeding from CWS into HWS do still work so I can turn those off to reduce flow but the Grotherm pump is fed from Essex flange located about a foot below top so there would still be some water loss - I could of course just drain tank down to the Essex using drain cock at bottom or use a bucket

Unfortunately the gate valve that isn't working is fitted about 1 inch from the Essex and horizontally so is no doubt filled with all sorts of cr*p. Am reluctant to remove this as the Essex doesn't look to be in great condition and I can otherwise see a full HWS cylinder replacement looming!

*for some reason the HWS has two CWS feeds in at bottom - one either side and both 22mm. Have not seen many tanks with two in-bound feeds and can only assume it is because there was previously a pretty powerful pump (Stuart Turner 4.0 bar) which would draw HW pretty quickly and need replenishing quick too?