Thermal Store Heating Up Cold Feed Pipe

[iainf3]

Hello, I have just installed a vented McDonald 250L thermal store, it is for multi fuel but currently just connected to a standard oil boiler in the garage which is fully pumped to the TS, the system has two pumps both basic 3speed Grunfoss, one on the boiler return and the other on the CH flow both set at the lowest setting.
The F&E tank is in the loft approximately 430mm from the top of the TS to the bottom of the 20litre tank, this in turns uses 15mm cold feed pipe to the bottom of the TS. The expansion is 22mm pipe and run up to approximately 520mm to the top of the bend to the F&E water level.
When on DWH only it works well and heats the tank in no time but when the heating kicks in again heats the radiators effortlessly but starts to heat up the cold feed pipe to the F&E tank. If left on long enough heats it all the way to the tank and assume if left on long enough would heat it as well which is the concern. The 22mm expansion pipe would seem to be sucking in air when this is happening. Attached is a sketch of how it is connected. Any help would be appreciated

 

[iainf3]

Hello, from your last note, I had look at the AAV and found a new one in the garage and have stuck it onto eliminate all threats. Will try it on now and see if that helps any.

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

 

[iainf3]

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

Hi JohnG, did you see the sketch of the radiator connections in the previous post, does that make sense about opposing tees or is this not worth bothering about. Many thanks for the help to date

 

[John.g]

I have two rads upstairs connected exactly the same way and even have a 1.5M length of 15mm from the T to the main 22mm return pipe, these rads work fine in my 50 year old open vented system.