Retrofit Automatic Bypass

7 Mar 2005
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United Kingdom
My system uses an Ideal FF270 with TRVs on all but 3 small rads (2 in the hall and 1 in the loo) and seems to have 2 separate 2-port valves for CH and HW. The installer fitted a gate valve bypass in the airing cupboard which he set to about 4 turns open.

Now the system works OK i.e. there is no noise and the radiators get warm eventually. However, I wondered if there was any advantage to retrofitting an automatic bypass. When operating, the boiler does seem to cycle quite a lot even when the rads are cold and it takse quite a while to get all the rads hot everywhere (I think they are balanced correctly though). I have read that an automatic bypass will get the rads hot quicker and more efficiently, possibly saving money in the long run

But is it worth it ?
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Firstly you need to identify if the current bypass is actually the reason for the slower heating and increased cycling.

from cold turn your heating on and close the manual bypass fully and report back how the system operates then.
Also I cant rememebr off the top of my head but does this boiler even have a pump overrun feature? I dont think it does which renders any bypass pointless is you have a couple of rads that you keep on at the valves where there are no TRVs
Reading the blurb, yes, I think the boiler does have an overrun feature but I can't be sure. I'll try the method of closing the bypass valve completely to see how the system responds but of course if both 2 -port valves are closed there is a time when the pump has nowhere for the water to go. If I continue to use the gate valve, is there an easy way to check if it is providing enough flow when both the CH and HW valves are shut ? It seems a bit hit and miss when I have read up on the methods advertised. Obviously with both CH and HW valves closed then the bypass needs to allow quite a bit of hot water through to prevent pump strain and/or boiler problems. So, that no heat required bypass setting doesn't work when both CH and HW valves are open even though it has a smaller pipe bore. I can see the advantages of an automatic bypass valve but is it worth the effort to retrofit. At a cost of say £30-£40 plus fitting, what is the timescale for recovering the cost versus turning on the heating system earlier and running for longer ?
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of course if both 2 -port valves are closed there is a time when the pump has nowhere for the water to go.

Not if theres no pump over run, in this case when the valve closes it will stop power to the boiler and boiler and pump will shut off.

Im 99% certain there is no pump over run on these boilers, rendering the bypass pointless.

Turn heating on, see pump running, turn heating off, if the pump goes off straight away with the boiler then you dont need a bypass.
You are correct. The pump comes on and off with the heating without any overrun. Does that mean it's OK to close the bypass completely as I have 3 small rads without TRVs ?

But if it was mine then I would actually add a delay relay to provide a pump over run and over a year or two the heat recovered from the heat exchanger will give a slight improvement in efficiency.

It would also increase the life of the fan which operates in a very hot environment which tends to prematurely dry out the bearings.

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Yea shut bypass completely, and see how well rads heat, cal leave it closed after that

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