hot water heat exchangerS 1 works fine other has problem

[John Mitchell]

Hello I hope somebody is able to offer advice. I have 2 boilers each having heat exchanger fitted to hot water cistern. The gas boiler does not heat the hot water, this is the problem, I will explain later. The multifuel SF boiler heat the water extremely well, connected to the standard side fitted heat exchanger via 22mm copper. However the gas boiler connects to a heat exchanger fitted into the immersion heater boss vertically top of cylinder. The device has been there for decades, unused, so old it don't have octagon fitting, has 4 slots for huge C spanner? 2 x 15mm pipes both look identicle. I connected flow and return to said pipes, result: dissapointing, very poor heat exchange. Thus, I think I've connected in reverse order? Does this sound to be the reason heat exchange is pathetic? I cannot understand the principle of how a top fitted heat exchanger can work to be honest. Side fitting is obvious to me, water convection principle of hot water rises. Please if anyone out there has seen or uses a top mount explain to me. I don't wish to reverse connections unless I know this will resolve the problem. Because its a lot of work involved to drain heating system and hot water system! Thanks friends, I wait in anticipation.

[simon@hwch]

If this is a sidewinder fitted into an immersion boss, then they aren't very effective.

If you want help I suggest you describe your system in greater detail, for instance, there are thousands of gas boilers and hundreds of stoves.