Fitting Cylinder 'Stat On Primatic System

[Stuart]

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

[Doctor Evil]

The flow and return pipes to the primatic cylinder must have "no" valves on them of any sort. "Take the valve off ASAP". The cylinder is also the F&E tank and must have a clear way to the boiler in both flow and return.

Have a normal electric cylinder stat to keep the boiler from cycling when DHW only is on. A boiler interlock. When the CH is on you get DHW whether you like it or not and the cylinder temp is determined by the boiler stat which may be too hot for DHW. To have a set DHW temp also have a blending valve on the DHW draw-off.

So, you need a low pressure DHW blending valve and a normal cylinder stat.

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[Stuart]

So what sort of set up is displayed here then ?.

gravity valve with the two connections for gravity systems not the three port one .. Stuart ps..The valve isnt fitted yet anyway so no need to worry on that score ..

[Doctor Evil]

is not a primatic setup. NO VALVE, of any sort should be on the primary flow and return of a primatic cylinder. Take the valve back, and get a normal cylinder stat and DHW blending valve.

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