Loud clunk from motorised valve

[jo23483]

Exactly as was suggested (thanks all) the valves were the wrong way around. These have been reversed & the clunk is gone.

The auto bypass was replaced its low cost meant it wasn't worth not doing it.

Setting the bypass raised a question. The boiler a Greenstart 24Ri has no minimum flow rate in its specification. The pump, a Grundfos 15-60 130 needs to be on setting 2 to heat up the remotest radiators. The pump says it can generate over 0.45 bar at its lowest throughput. Practically the bypass pipes feel hot no matter what setting I use (0.2 - 0.5 bar) which seems consistent with the pumps capability.

My question, Does it seem reasonable to leave the bypass set high (say 0.4) to minimise bypass flow? My concern is this is miles away from the default 0.2 setting and presumes the boiler really has no minimum flow (even though I suspect the flow never stops at 0.4). I have no means of measuring pressure in the system.

 

[John.g]

If the pump you have is a UPS2 (5M on speed 2) then a setting of 0.45 would be quite OK IMO as the ABV will still give a bypass flow of ~ 0.3m3/hr when TRVs shut in or zone valves shut which should be quite adequate but if the system is happy with 0.4 with all rads heating then I would leave it, only downsude of this is you may be running with a higher boiler return temperature which will have a small impact on efficiency.

 

[jo23483]

I'm not sure how to read that diagram, but the pump is the older UPS with spec as below, which also seems easier to read. Its pushing 1 m3/hr at .4bar, and just misses reaching 0.5 bar hence the 0.4 ABV setting. Your answers gives me confidence that 0.4 is ok - thanks.

 

[jo23483]

n.b. I now see the new spec is just a truncated version of the old spec. I don't understand the orange lines.

 

[John.g]

The UPS2 has proportional pressure PP settings as well which reduce the pump head as TRVs throttle in or zone valves close, u fortunately all a bit low to be really useful, the big difference is the 3 constant curve settings which are partially constant pressure pressure which make setting up a ABV quite difficult, unlike your model as head falls as soon as the flowrate increases, nobody has told me yet why all A rated pumps behave like this, just have a look at the UPS 3 pump curves!!

 

[jo23483]

Thanks for explanation, If understand properly, in pp mode (where head drops as flow demand falls) I would have thought that use of an ABV to be near impossible, not difficult. As the ABV looks to relies on an increasing head to be turned on.

 

[John.g]

Yes, unless you are prepared to suffer with very high boiler return temperatures, its bad enough even on constant curve mode where you are trying to set it up effectively in constant pressure mode, I don't require a ABV with my oil fired boiler.