I live in the UK and I have a Medway Main water heater supplying all the taps in the house and a shower. The shower has a Thermix Mk2 shower valve and a Deneve water governer in the cold pipe between the water heater and the shower. After the shower has been running for about a minute the flames in the water heater will die down and then this is followed by a noise and vibration from the Thermix valve that sounds and feels as if a piston is moving violently inside it every few seconds and this eventually becomes a loud whine.
I would get a new mixer valve except that the problem may not be in the valve. Can anyone offer suggestions please. I cant find out who manufactured the Thermix so as to ask them.
Thanks Ron Etherington