TL;DR

Getting a Midas Plus squirting properly again is very easy once you learn the secret of removing and cleaning the thermostatic cartridge. A simple procedure due to some great design, but one that isn’t documented anywhere that I could find.

Background

In just over a year since I had a new shower fitted as part of an en-suite refurb it went from ‘Oh yeah!’ to ‘meh’. I’ve had Aqualisa showers at home for over 20 years, which I guess makes me a loyal customer, but in that time I’ve needed a few replacement thermostatic cartridges – generally because the flow rate has become a bit useless.

Checking filters

The trouble shooting guide in the installation instructions suggests three possible causes for poor flow rate – twisted hose, debris in shower head, and debris in filters, with ‘check and clear as necessary’ as the action to take. I knew it wasn’t the first two, as flow was fine if I turned the thermostat to cold. So I set about checking the filters, which meant taking the mixer bar off its mount.

• First I turned off the water supply
• Then I taped over the fixing nuts with electrical tape (as they’re shiny stainless steel, and I didn’t want to scratch them with my dirty old adjustable spanner [they’re 29mm, and I don’t have a regular spanner that big])
• After loosening the nuts I was able to pull the mixer bar away and remove the filters. The cold filter was clear, but the hot filter did have quite a large crystal deposit in it, which I rinsed off with a jug of water.

All of this made absolutely no difference. The shower flow rate was still poor.

The cartridge

I called the Aqualisa support team for help, and after talking through the problem they offered to send me a replacement thermostatic cartridge. This led to a follow on question from me about how to fit it once it arrived? The support person said to follow the installation guide, but I’d already been through that, and it makes no mention at all of cartridge removal and replacement. She then told me to start by taking the end cap off the control. When I went and tried that I soon discovered that isn’t how to get the cartridge out.

Picture of cartridge from Aqualisa website

I then did what I perhaps should have done in the first place. I took to YouTube, and found this video ‘Thermostatic cartridge: maintenance, replacement and calibration‘, which showed me that the cartridge is held in by a (very well hidden) grub screw on the bottom of the mixer bar. All I had to do was:

• Turn off the water supply (IMPORTANT – the water on/off on the left hand side of the bar simply acts on the cartridge, so if you take it out without isolating the supply first the cartridge will fly out and then water will gush from the mixer bar).
• Undo the grub screw on the bottom right hand side of the mixer bar with a 3mm hex bit
  
• Pull the cartridge out
• Rinse away any debris using a jug of water
  

  Other side of cartridge showing where grub screw fits

Once I popped the cartridge back in the shower was as good as new.

Crucially there was no need to remove the end cap and mess around with the thermostatic calibration.

I have questions

Once you know where the grub screw is, the simplicity of removing and refitting the cartridge stands out as a wonderful piece of design. Somebody thought very hard about how to make this as easy as possible; and then somebody else decided to exclude any mention of the grub screw and the cartridge from the instructions. Given that in the past Aqualisa have provided detailed instructions for the much more complex process for removal and refitting of earlier designs it seems really odd that they managed to make everything so much better, then chose to keep the details to themselves. This must result in a higher than needed support burden, and associated drag on profitability, which I find utterly bizarre.

Also the filters on the cartridge itself are (by my estimation) finer than the main inlet filters. So ‘check and clear’ for the filters should definitely mean both the inlet filters and the filters around the cartridge itself. Again I’m guessing that’s by (very good) design, and then somewhere else a decision has been made to withhold crucial information :/