Auto bypass valve/pump settings

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Hi all,

I thought I'd got my head around my central heating system but I've just discovered an auto bypass valve, the workings of which I don't have a clue about if I'm honest so I'd be really grateful for some help!

I have a Vaillant Ecotec 428 heat only boiler, unvented system with hot water cylinder. All radiators have TRVs. The boiler is downstairs in the utility room. The bypass valve is in the airing cupboard with the pump, that I have recently swapped over for a Lowara Ecocirc 25-8/130 variable speed.

The bypass valve appears to just be set on it's lowest setting. From what I gather this might mean that water is circulating in a loop unnecessarily? Is there a simple way to set it up correctly? I have checked the specs for my boiler and it says it needs a minimum flow rate of 20.3 l/min. I had set my pump on the PP3 setting which is 1.30m3/ph, or CC2 setting which is 1.29m3/ph. The rads heat up fine on both these settings.

I've attached some photos of the pipework, valve and the pressure loss graph for my boiler if that's relevant
 

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You shouldn’t have a TRV on the rad in the room where the room stat is. If you do, it should be set on max. I set my ABV up by closing down the bypass valve, closing off most of the rads and turning the heating up to max, letting the rad get nice and hot. I then started opening the bypass valve a turn at a time until I could feel that it had opened (as the bypass pipe got hot). I then tightened it up by half a turn and that was it. I have my pump set on the slowest speed. Put all the rads back to how they were and once the system has cooled down, turn the heating on max again and once the system is getting hot, turn the room stat down. The zone valve should shut off and the ABV should open fairly soon after that as the boiler runs on for a bit. That’s how I did mine anyway!
 
You shouldn’t have a TRV on the rad in the room where the room stat is. If you do, it should be set on max. I set my ABV up by closing down the bypass valve, closing off most of the rads and turning the heating up to max, letting the rad get nice and hot. I then started opening the bypass valve a turn at a time until I could feel that it had opened (as the bypass pipe got hot). I then tightened it up by half a turn and that was it. I have my pump set on the slowest speed. Put all the rads back to how they were and once the system has cooled down, turn the heating on max again and once the system is getting hot, turn the room stat down. The zone valve should shut off and the ABV should open fairly soon after that as the boiler runs on for a bit. That’s how I did mine anyway!
Great, thanks I will give that a go. I did turn it up a bit to 0.3 and it seemed to adversely affect the flow to some of the radiators which I don’t really get but will have another look at the weekend. Another slight oddity is that I was looking at the boiler installation log entry (from 2006) and it says an ABV wasn’t fitted, and it doesn’t look like an old fitting to me…
 

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