Hansgrohe new Thermistor Cartridge - Serious Buzzing during mixing

[monty]

I have a brand new Hansgrohe Thermobalance II assembly with a new thermostatic cartridge part #94282000 - sent to me by Hansgrohe

The new thermostatic cartridge is now part plastic, where the old one was mostly brass.

My problem with the new one is it creates a really loud buzz-screech when the water temperature switches to hot while filling the tub - It doesn't happen with the shower side and this never happened with my older version - the old Thermobalance housing is bad - so the entire assembly was replaced. I have flushed the new Thermobalance and there are no debris in the lines.

I could use my old thermostatic cartridge but it has some problems going cold all of a sudden - so I think it is worn out too.

Any tips or ideas???

Thanks in advance

[monty]

I think I might have solved this problem by putting a pressure regulating valve on my incoming water line to the house - I had over 100psi incoming pressure and use a tankless hot water heater that apparently was creating too much of a pressure difference between the cold and hot supply sides. With reduced incoming water pressure the valve seems happier and works better in 2 days of testing.

[EuroPlumber]

Hi Monty, The new version 94282000 cartridge is made of plastic to reduce the buildup of lime and mineral deposits which can cause the moving parts to seize up over time. Your correct that the valve was howling due to pressure differential. The cartridge was trying to pinch down the cold inlet (High pressure) while keeping the hot inlet (low pressure) open. The unequal pressure puts additional load on the low pressure side as it tries to compensate for the added pressure in the hot side.

The flow rates between the shower and tub spout bear this out. The slower flowing showerhead maintains more back pressure as it demands less flow through the instant water heater. Less flow through the water heater means less restriction and lost PSI.