Bypass Valve set-up (Apollo in particular)

[stevesey]

Balancing problems. As a rule boilers are meant to have a temperature difference of 11ºC - 20ºC between the flow and return at the boiler, see Manufacturers instructions. This is achieved by careful adjustment of a by-pass valve which effectively short circuits some of the water to avoid a dramatic rise in temperature resulting in noisy operation. This is often critical for some older boilers such as the apollo.

Just read this in the FAQ as I have a Thorn Apollo 50 which has never been particularly quiet it caught my attention. Could enyone enlighten me about how I should check/adjust the bypass (pipe thermometers?) and why so critical on the apollo?

Currently the bypass is almost closed as we have two towel rails in the circuit that have locksheilds on both ends. House is a mix of TRVs and standard radiators - I'd assumed the towel rails would provide enough bypass. Indeed I have the system balanced so that the towel rails don't get really hot until some of the TRVs have started to close.

Also what about an automatic bypass - these seem to make sense from the viewpoint of only bypassing when the enough of TRVs have closed. But will this affect the "critical" nature of the bypass set-up on an Apollo.

Whilst writing this I started thinking about the option of a constant head/variable speed pump - I see Grundfos have one (Alpha+) any experience of these?

 

[stevesey]

Bump

 

[ChrisR]

CHeck the Alpha pump instructions - you adjust it.

 

[stevesey]

Yep - read the instructions. Missed one on ebay today at £21.00 + £10.00 P&P.

Any thoughts on Slugbaby's comment the the FAQ about why the bypass is so critical on the Apollo?

Interestingly I finished the bathroom and the weekend - after fitting the towel rail I closed the bypass completely and wacked the pump to 3 (14 rads in all to suppy). Anyway long and short is that boiler is now quieter (less roar) - might have something to do with draining a bucket of water and topping up in order to change the valves in the bathroom.