Shower Water Getting Colder During Shower (linked to boiler)

[mtaylor39]

I've got a situation where a Mira Thermostatic shower starts off at the right temperature but during the course of it being on it gets cooler. Not cold, but gradually gets colder. If you turn the shower temperature up it gets hotter, but then the temperature starts to reduce again. I get probably 2 minutes before it gets cooler and then 1 minute every time I turn it up.

The thermostatic shower has been replaced and it's still doing it, and probably getting a bit worse. The taps in the bathroom, kitchen and utility room seem fine, but I think the bath tap is also doing something similar. I think this is because the flow of the water is greater for the shower and bath compared to the taps.

The boiler is a Viessmann Vitodens 111-w 32kw storage combi and was installed in November 2022, and the problem has only been in the last month or so. It's under warranty, but Viessmann are saying it's nothing to do with the boiler, but the system itself. As the shower has been replaced I find it hard to believe it would be the pipes. I feel the issue could be a diverter value, heat exchanger or something with the storage element (thermometer?). But wondered if any of the people on this forum could suggest what it could be? Are Viessmann just trying to get out of the warranty obligations?

Happy to provide any more info if needed.

Thanks!!

 

[Chuck]

Have you checked that the hot and cold feeds to the shower have the correct 'polarity', i.e. are going to the correct inlet and have not been swapped? Not likely to be the problem but it does happen so is always worth checking.

How many litres per minute is the shower specced at / delivering? (Use a measuring jug and stopwatch to measure this)

 

[mtaylor39]

Have you checked that the hot and cold feeds to the shower have the correct 'polarity', i.e. are going to the correct inlet and have not been swapped? Not likely to be the problem but it does happen so is always worth checking.

How many litres per minute is the shower specced at / delivering? (Use a measuring jug and stopwatch to measure this)

Thanks Chuck - I should have said that both the shower and boiler have been in place since 2023 and this is a new issue that is happening. So it's been fine until recently.

I've also notice that after myself and my wife has showers one after each other and then I used the taps on the sink the hot water from the taps was lukewarm too. I left it a few minutes and the water was hot again. It's like I've drained the tank and it can't keep up, but this hasn't been an issue previously. Could it be the heat exchanger being less effective?

 

[Chuck]

I've also notice that after myself and my wife has showers one after each other and then I used the taps on the sink the hot water from the taps was lukewarm too. I left it a few minutes and the water was hot again. It's like I've drained the tank and it can't keep up, but this hasn't been an issue previously. Could it be the heat exchanger being less effective?

How many litres per minute are the showers delivering and for how long (in minutes)? (Use a measuring jug and stopwatch to measure this)

Have you checked that the DHW setting on the front of the boiler has not been turned down?

 

[mtaylor39]

How many litres per minute are the showers delivering and for how long (in minutes)? (Use a measuring jug and stopwatch to measure this)

Have you checked that the DHW setting on the front of the boiler has not been turned down?

Thanks Chuck - turns out it was a blocked heat exchanger. Once that was cleared out it's all back to normal.