I have a pumped CH/Gravity Domestic HW utilising a Primatic cylinder .
I replaced the gaskets on the Boiler heat exchanger and also replaced
the cylinder connnectors as they were the wrong type and prone to
leaking .
Previously the DHW used to get very hot so I have a Danfoss-Randall
cylinder stat which is a valve with a sensor,similar looking to a TRV
the valve sitting in the flow or return domestic pipe and the sensor
is strapped to the cylinder .
I've never been able to get my head round how this sytem works .How
does the water in the CH part get topped up as it must need due to the
water dissipating away . I presume there must be some mechanism in the
coil part that allows this while not allowing the CH and DHW to mix .
If this cylinder stat closes when the water reaches the set
temperature does the flow within the gravity part just stop
completely until the temperature reduces and the valve opens again
....I don't know how long this would be ?
Stuart