Hydronic Kick Space Fan Heater Removal

[waternightmare]

Hi, My system is 12 years old, open vented, pumped y plan, ideal RS40 boiler, house has solid floor downstairs so rads are all on 10mm plastic microbore, fan heater on 15mm plastic.

I have a myson kickspace 500 hydronic fan heater in my kitchen and I am looking to remove it and just need to know the best way to go about it or if possible using the same pipework change it for a radiator.
Each pipe into the fan heater has an isolating valve so after removal I want to join these pipes together with a connector but should I then leave the valves open or shut?
I have tested by turning off the isolating valves on the two pipes to the heater to check the system still functioned with it off and it did so am I right in thinking that the fan heater will be connect to the flow and return on the primary circuit just like all the radiators will be but using 15mm instead of 10mm?
If after removing the fan heater I join the two pipes together and leave the circuit open creating a loop would that cause a short across the system or would leaving the valves shut breaking the loop, increasing flow round the rest of my system?
I have also just bought TRVs to fit on the upstairs radiators and have no auto bypass so I am concerned that doing this as well will increase system flow or is that nothing to worry about.

 

[echoes]

have tested by turning off the isolating valves on the two pipes to the heater to check the system still functioned with it off and it did so am I right in thinking that the fan heater will be connect to the flow and return on the primary circuit just like all the radiators will be but using 15mm instead of 10mm?

Fan heater will most likely be connected to flow and return on the CH circuit (not the primary).

Don't join the flow and returns of the removed heater. Just close the valves and leave the pipework in place for when you get the radiator.

I have also just bought TRVs to fit on the upstairs radiators and have no auto bypass so I am concerned that doing this as well will increase system flow or is that nothing to worry about.

No bypass needed on a y-plan if there is one radiator with 2 lockshield valves (in the location of the room thermostat). All other radiators can have TRVs.