I have three mixer showers in the house, all appear to run from the same shower pump and have done for at least 5 years with no issue (it’s not often more than one is in use at a time). The Mira Excel shower has started going tepid after about 9-13 mins, the temperature doesn’t come back when it’s left on. The en suite bathroom shower is absolutely fine, totally hot water for 15mins plus. But when the Mira one has gone cold, the one in the en-suite is then also cold when turned on. The Mira cartridge has been changed by a plumber, and the temp/pressure is generally better (I used to have to have it on 1 for a normal temp shower, now 7 is about right), but it still goes cold after the same time. The plumber is totally bemused as to what it can be! Can anyone help? For info, it’s a tank boiler; there’s still plenty of hot water coming out of the sink taps when the shower has gone cold; it started about 3 weeks ago, I hadn’t had any work done or anything, it just started.
Are you a tradesperson and able to answer this question?
I dare say it a combination of factors & unlikely 1 definitive cause.
1. The stored cold water will be much cooler during periods of very cold weather & thus needs to mix with more hot water to achieve any given set outlet temperature.
2. The Mira Excel maybe allowing a higher flow rate than the other showers in the house. If the thermostat was working & controlling the water temp then it was a bad decision to change the thermostat in view of the fact the other showers had no HW either. Change your plumber M Excel cartridges are expensive.
3. I would suggest the pump takes its supply via an Essex flange on the side of the cylinder so a small volume of hot water remains above it supplying taps. A Surrey flange would allow use of nearly all the stored HW but little would remain for the taps.
4. The cylinder thermostat may have been turned down, accidentally knocked or moved. You can turn this up to a max of 60 degrees at a push but 58 is really as high as is desirable for most situations. Remember the cylinder will get hotter at the top & most pumps & other components are usually rated below 65.
5. The HW recovery time could be taking longer due to point 1 & possible scaling of the heat exchange coil. The heating system will also be competing for output from the boiler so at times of higher demand then recovery may take longer. Try turning up the boiler thermostat. You could also consider using the immersion heater too if you have one.
6. Try using water saving spray sets to restrict water usage on your showers.
To summarise, it sounds like you are maxing out your HW system to begin with. That coupled with extreme cold conditions will be the root cause IMO. Consider upgrading to a larger HW cylinder or maybe go unvented. However with a few mods & sensible use this probably won't be necessary.
Hope this helps, Martin.
I would check the cartridge again the mixer one as I have had this once before I have had 3 new cartridges which have failed straightaway then my next point of call would be the pump has five years is quite a long time to settle for showers hope this helps
