Grundfos Alpha 2 15-60 130 Setting?

[woodpeckerx]

I have a British Gas 330 boiler with a Grundfos Alpha 2 15-60 130 pump, 15 rads plus vented cylinder.

Trying to figure out the correct pump setting, the manual says recommended mode is Auto Adapt but this only runs around 6W and doesn't seem to give enough flow (does Auto Adapt actually work?).

Alternative recommended modes are PP1 or PP2, in PP2 it runs about 11W which would seem to give a flow of around 900 l/h from the graph? AFAIK boiler is set to default 18kW and needs min flow of 774 l/h

What should it be set to?

 

[Johntheo5]

The only pump I have seen working in Auto adapt mode is a Tucson running at ~ 23/26W.
Grundfos PP modes are also far too low, I make out 11W on PP2 as ~ 500LPH @1.8M.
If my curves, below are correct then suggest CP1 as that should give ~ 645LPH. Alternatively, maybe CC2, post back your readings on both and if to hand, the pump curves that you have.

 

[Johntheo5]

These are for the Alpha 2L, are they the same as yours?

 

[woodpeckerx]

I'm getting a bit lost with it, these are the curves I was looking at, just re-tested and I'm getting 9W on PP2, with 1 TRV open and a towel rad with no TRV I'm getting bursts of heat but the ABV is opening despite setting it higher.

 

[Johntheo5]

You are getting 0.35m3/hr, 5.8LPM @ 1.7M head, if the ABV is working properly then any setting above 2M (0.2 on the index) should mean that its not bypassing anthing. What index is it set to??

 

[woodpeckerx]

What index is it set to??

It's a Tower ABBV1 (brand new just installed it) its set to 4.5 at the moment.

 

[Johntheo5]

Is it hot on the downstream side say a foot or so away from the ABV?, if so then either its knackered or a bit of crap has got trapped under the seat. The only two settings that will cause it to bypass at 4.5M is just maybe CP2 at 4.5M and CC3 at > 6M will certainly cause bypassing.

 

[woodpeckerx]

Is it hot on the downstream side

Yes it's getting pretty hot on the downstream, I think it is defintely bypassing.

 

[Johntheo5]

Unfortunately then you will have to at least remove the head and see if something trapped underneath so will probably require at least a partial system drain down, probably best to have another one at hand, I would prefer a Honeywell DU144 or the like, you can allways return the new one if old one OK after clean out or whatever?.

 

[woodpeckerx]

Re-tested again today and the ABV is working fine, I re-calibrated it and then adjusted it.

I'm still pulling my hair out with the pump and settings though.

The whole system has brand new Drayton auto balancing TRVs, all set per the instructions based on radiator outputs and using setting for dT 20 degrees.

Testing today, I closed off all rads except 2, both had the balancing valves set and no TRV fitted, lockshields fully open. In this case the boiler very quickly ramps to 60 degrees then switches off for quite a few minutes until the water temp drops. It seems like the boiler is getting too hot too quickly and switching off, is this lack of flow?

I tried all pump settings and it was the same, phoned Drayton and they suggested upping the valve settings to the dT 15 degrees but made no difference.

Any suggestions what could be going on here, I had the system drained recently but have bled everything multiple times and even loosend the CH/HW valve bodies but only water came out, could I have air trapped somewhere in the system?

 

[Johntheo5]

You can tell exactly what the flowrate was with that smart pump, just shut the ABV, run the pump on say CP1 (3M) and read off the power and then read off the flowrate from the pump curves, that will give a good feel for whats going on.
Assume your two rads have a combined output of 3kw at their full rated output, if so then the boiler will probably still cycle unless its min output is < 3kw.
If you have a few readings post the mode and watts but with the ABV shut.

What model Drayton TRVs?.

 

[Johntheo5]

As a guide, if you use a flowrate of 1.0LPM per kw (rad) this is a dT of 14.33C, so those two rads IF ~ 3kw will flow 3LPM (0.18m3/hr) and the pump will have a power output of ~ 14W on CP1.

 

[woodpeckerx]

CP1 is reading 14W ABV shut, the open rads are about 2.5kW total

What model Drayton TRVs?.

All valves are TRV4 auto balancing, heads are off for testing but most of them will be the Wiser smart heads once I'm sure its all working ok.

 

[woodpeckerx]

14W on CP1

It reads exactly that!

So is this normal? Trouble is my last property had a 20 year old non-condensing oil boiler, it was pretty much either on running like a rocket ship or off. I'm not used to Gas, do gas boilers switch on and off like this?

 

[Johntheo5]

Yes, I have a 18 year old oil fired boiler myself which because (all oil fired boilers) it cannot modulate, spends all its life cycling on/off, gas boilers do modulate but most are ~ 5kw minimum, some are "worse" some better. Also, unlike a oil fired boiler which will refire as soon as the water temperature is ~ at its setpoint minus 8C, gas boilers have a anticycle time of anything from say 3 minutes to 10 mintes before they refire.