Fitting thermostatic valves to open heating system?

[Jack67]

I have been told that I cannot fit thermostatic valves to an open heating system as it would cause the water to flow back into the expansion tank. The only way would be to convert my present system to a sealed system?.

Is this correct?.

 

[sotal]

I'm no expert but what do you mean by open system?

From what I gather a sealed system is what you have with a combi boiler, and a vented system is what you have with a conventional boiler.

I have a fully pumped vented heating system with TRV's on the rads