Grundfos Alpha 2 15-60 130 Setting?

[Johntheo5]

Sorry, Misread that CP2, see corrected above.
So yes flow extremely low for a coil with very large pipe diameters?.
Pump probably OK??. but is it likely that those pipes are scaled up or the coil itself??.

I still think that pump head should be removed, what do you think?.

 

[fixitflav]

HW seems fine, CH causes boiler cycling and occasionally has given an F26 flow warning also a couple of full trips with red light on.

It seems to me there is not enough flow through the CH so the boiler heats too quickly and cycles, manual states min flow must 774lph.

It seems the HW cylinder gets more flow than the CH, which is a bit odd. Are you sure the HW motorised valve isn't stuck part closed, or some other restriction in the pipework?

 

[Johntheo5]

My system is similar to the above (healthy) one in that the coil flow is > the sum of the rads, presume the coil just acts as a bypass?

 

[woodpeckerx]

Are you sure the HW motorised valve isn't stuck part closed

The valve is fine, I had to take if off when I was fitting the ABV, the valve rotates fine, motor is fine, didn't look too dirty either.

 

[fixitflav]

My system is similar to the above (healthy) one in that the coil flow is > the sum of the rads, presume the coil just acts as a bypass?

I agree it's a shorter, straighter route through the coil, but unless there's some restriction in the CH circuit I'd expect there'd be enough flow for the boiler to work properly. All the rads in parallel with TRVs open shouldn't give much resistance.

 

[woodpeckerx]

Pump probably OK??. but is it likely that those pipes are scaled up or the coil itself??.

I had the 22mm section part where the HW valve is to T in the ABV, no scale and didn't look too bad, the F&E is fed from a softened feed so hopefully that reduces scale.

The cylinder is date stamped Jan 2021 so quite new, don't think the coil has any restriction. The only other possible restriction on the HW is the gate valve on the coil return but I've wound that fully in and out, it looks new, probably replaced within the last 2 years at the same time as the tank.

 

[woodpeckerx]

All the rads in parallel with TRVs open shouldn't give much resistance.

Except I have these Drayton auto balancing valves fitted which definitely restrict the flow on the CH side.

But this doesn't explain the quite low wattage readings I am getting from the pump when HW or ABV open, it seems I'm not getting good flow.

 

[woodpeckerx]

I still think that pump head should be removed, what do you think?.

Nothing to lose I guess, another fun evening in the airing cupboard

 

[Johntheo5]

I did hear of a pump that gave the same closed valve power readings with the pump discharge valve fully opened or fully closed and the impeller was choked with debris. Yours is pumping some water but if the isolvalves are of the gate valve type with a spindle you could just shut the discharge valve for a few seconds and take readings to confirm that they read as per graph, my closed valve readings were exactly as per the graph.

 

[Johntheo5]

Except I have these Drayton auto balancing valves fitted which definitely restrict the flow on the CH side.

But this doesn't explain the quite low wattage readings I am getting from the pump when HW or ABV open, it seems I'm not getting good flow.

Except that the boiler Hx may be choked.

 

[woodpeckerx]

you could just shut the discharge valve for a few seconds and take readings to confirm that they read as per graph

Took the 4 allen screws off the pump and pulled it apart but its sealed behind so didn't get to look at the impeller, wasn't sure if it was a good idea to prise it apart so put it back together.

With the discharge gate valve closed I get:-

CP1 = 11 (about 2 lower than graph)
CP2 = 26 (about 4 higher than graph and same as when open)
III = 30 (about 4 lower than graph)

Can you deduce anything from that?

Except that the boiler Hx may be choked.

I hope not and guess there is no way to test that?

 

[Johntheo5]

I have only ever split one of the older 3 speed only pumps, there was a SS diaphragm on these I think which i carefully prised up and was able tp pull the head off. Again. on the older type, with the pump removed, you can see the impeller at the discharge port and on the old one I have here its possible to push a narrow tie wrap through the impeller vanes to prove them clear which may be enough?.

Those pump readings certainly don't compare to mine which read exactly as it says on the tin.

Boiler Hx
There is possibly a bit messy way of testing it but I have never seen it mentioned, you would need to disconnect the flow and return at the boiler, connect the mains with a isol valve and a accurate pressure gauge with as low a range as possible, maybe 0 to 3bar, to the boiler return, open the isol valve to give say 0.3bar and measure the amount of water that flows from the boiler flow end.

 

[woodpeckerx]

If the Hx was choked wouldn't I be getting a lot of noise and kettling from the boiler, when HW is on the boiler sounds smooth and quiet, with these Drayton valves open a bit wider and just the CH on the boiler runs quiet and smooth as well.

Those pump readings certainly don't compare to mine which read exactly as it says on the tin.

I'm also noticing as well that I have to really wind open the ABV to get it to release, like there is not enough pressure to push it open, it doesn't open until I get down to 1 on the scale.

I just did another test with, HW, CH and ABV open, pump readings are the same.

I could buy a new pump, what do you think?

 

[Johntheo5]

If the Hx was choked wouldn't I be getting a lot of noise and kettling from the boiler, when HW is on the boiler sounds smooth and quiet, with these Drayton valves open a bit wider and just the CH on the boiler runs quiet and smooth as well.

Don't really know but I would leave this "job" as a last resort.

I'm also noticing as well that I have to really wind open the ABV to get it to release, like there is not enough pressure to push it open, it doesn't open until I get down to 1 on the scale.

I thought the boiler was rapd cycling on CH only even with the TRV heads removed and the TRVs fully opened?.

I just did another test with, HW, CH and ABV open, pump readings are the same.

I could buy a new pump, what do you think?

Yes, you could, of course, but not a big deal to remove the old one first and at least look into the ports?, or buy the new pump locally with the option of returning it if the old one has some obvious crap in it when you revove it and can clean it out. If you don't buy another Apha 2, ensure that whatever you purchase displays the power.

 

[woodpeckerx]

I thought the boiler was rapd cycling on CH only even with the TRV heads removed and the TRVs fully opened?.

I opened up the Drayton valves a bit more, they were at dT15, calculated a new set of values for dT12 and the boiler doesn't short cycle but the pump readings still seem wrong, rads still not getting super hot and also not very quickly.

I asked the mrs whether she thought the heating ever worked properly and she said nothing ever felt hot last winter, it could be the pump has always had an issue but it could also be the boiler. We just thought gas heating was different from the oil we had.

or buy the new pump locally with the option of returning it if the old one has some obvious crap in it when you revove it

All the local stockists seem to have the Wilo Yonos Pico 25/1-6 Pump which I guess would mean changing the gate valves as well (not a big deal) as the Alpha 2 has G1 threads, no one seems to stock the 15/1-6 locally.