So my mains connected shower does this odd thing where it will run normally for 2 or 3 minutes, then suddenly the pressure will rise and the water will go cold for 30 seconds, before returning to a normal temp and pressure for three minutes, then go cold again etc etc. This is nothing to do with toilets or other outlets being used, it is too regular.
Things to consider:
*If the temperature mixer is on full heat the problem does not occur. It only happens when the mixer is turned down slightly beyond that point.
*We have a combi boiler
*this issue only affects the shower - all other HW taps run from the same boiler and aren't affected.
*The shower is a thermostactic mixer and the whole unit was replaced due to this issue, but this didn't help
*If you drop the shower head below the level of the inlet to the thermostatic mixer unit the issue doesn't manifest
*Exchange plate in boiler was recently replaced.
It feels like there might be an issue with the cold water pressure struggling to overcome a blockage, but when it reaches a critical point it overwhelms the thermostatic mixer. Any sense in this?
