Grundfos Alpha 2 AutoAdapt is slow

[John.g]

Possibly, I suppose, but would only be a few LPM at most, I wouldn't run the pump on speed iii with a open vented system, suggest CP1 or CP2, presume header tank is full of water, have you tried opening the ABV? Also assume you have run both CH & HW together, is the boiler running continuously once there is a demand?.

 

[Marck C]

Ok so we had a frost last night so pretty cold this morning when i turned to system back on to monitor... took about 30 minutes before all the rads started to get warm and 50 mins before they were all hot to touch. I'm guessing it should be quicker than that..

Header has water, cant seem to shift the ABV (and don't want to force it) and yes have had both CH & HW running at the same time and the pump continues to run at 13W on Setting II (I'm using Setting II for continuity as that's what its been on and runs quietest on)

Yes the boiler seems to run continuously (barring one hickup when it first started up from cold).

No pressure gauges to check pressure

I've been studying the pipework to understand the how the flow works... The flow out of the boiler is as you'd expect very hot... the return to the boiler is just warm (I can keep my hand on it)

All of this seems (logically) to suggest the flow is low... Its so perplexing.

I have British Gas coming out tomorrow as a follow up on the previous job, I'll leave the system cold for them so they'll get to see how it starts and performs from cold.

Will feed back after the visit.

Thanks again for you help... much appreciated as always 👍

 

[John.g]

50 minutes wouldn't be indicative of a very poor circulation rate IMO, but certainly is reduced based on the boiler return temperature, but how this is achieved with that indicated 13W on speed ii is a mystery to me, last April/May you were getting 19W which made perfect sense as it's ~ 10.2 LPM at a 3M head., 13W indicates zero flow.

You might consider just doing one more test (takes only 10/15secs) just shut the pump discharge valve and see what the indicated pump power is, then fully re open it, as you are at it just confirm that the pump suction valve is also fully open.

Just thinking about the circ flow again, assuming your boiler modulates to say 5kw then you may be circulating as low as 2 to 3 LPM which probably wouldn't be measured by the pump power......so either air or a blockage (severe).

 

[Marck C]

Ok tried shutting and opening the discharge valve... no change to the 13W.. The other inlet side is fully open.

 

[John.g]

OK, thanks, sincerely hope not but if BG drained down the system to install that air vent and if dirty then there is a chance that the boiler Hx is blocked.

 

[Marck C]

😳 That doesn't sound good...

They didn't need to drain it down as the boiler is upstairs and the valve is at the highest point.

From a logic point of view its been running fine up and till the leak... so seems to have been an issue since the air bleed valve was leaking... now that i've worked out how the flow runs I see the valve sits on the return right above the inlet to the boiler...

could air be trapped in the boiler?

Do boilers have internal bleed valves that BG might try?

 

[John.g]

There should definitely be one inside the boiler casing on the boiler flow, I think these are normally closed after initial fill or refilling so BG can certainly check this out.
Even though the boiler is upstairs the header tank must be still higher so they must have shut a isolating valve (if fitted) on the cold feed to remove the air vent?

 

[Marck C]

Great will prompt em to check it...Yep there is an isolating valve to the header tank ... which is open

 

[Marck C]

Solved! BG came and the engineer removed the pump... turns out the impeller was sludged up with a coating of crud. She cleaned it off reinstalled and it now runs sweet and like a dream... Full speed on all settings without any of the noise that I had before.

The whole system seems to be running so much better...

Go figure...

Thanks for you help John.g
I learn something each time in on here and am always grateful for the comments.. 🥇👏

 

[John.g]

Solved! BG came and the engineer removed the pump... turns out the impeller was sludged up with a coating of crud. She cleaned it off reinstalled and it now runs sweet and like a dream... Full speed on all settings without any of the noise that I had before.

The whole system seems to be running so much better...

Go figure...

Thanks for you help John.g
I learn something each time in on here and am always grateful for the comments.. 🥇👏

Greatt news alright Marck, wouldn't have thought that was the problem, we can all learn from that. What setting and power output are you on now?

 

[Marck C]

So it was left running on III at 45W but I'm probably gonna try running it on CP2 (35W) Looking at your previous power/flow rates CP2 seems a good balance..

It runs quiet as a mouse on all settings now..

 

[John.g]

Can you try it on CP1 which was your last permanent setting and see if the power is 20W as originally, it will also tell us exactly the head and flowrate now.

 

[Marck C]

just nipped up and checked it..... It is 20W on CP1

 

[John.g]

That,s 10.5 LPM @ 3m which is 12.9 LPM @ 4.5m (35W), all adds up.
Even though it doesn't matter now I wonder was the pump just air locked as that problem appeared almost overnight, its a great pity that they don,t have a real vent screw like before.

 

[doitmyself]

I see that there is an ABV immediately after the pump, presumably because there are. separate zone valves for CH and HW. (A mid-position valve does not normally require an ABV as at least one path is always open.)

However, an ABV is incompatible with PP, CP and Autoadapt modes. You can only use a fixed speed. The correct setting for the ABV will depend on the chosen pump speed.

 

[John.g]

I would agree but I don't know of any true fixed speed, constant curve A rated pumps now ( the DAB Evosta 4-7M did/does appear to have them), if you take the above pump, constant curve 3 gives a constant head of 6M between 0 and 12 LPM (0.7 m3/hr) & constant curve 2, a constant head of 3m between 0 and 10 LPM (0.6 ms/hr), maybe a ABV can be set up, in practice, but how?.

 

[doitmyself]

I assume that "the above pump" refers to the OP's Alpha 2, not the DAB Evosta.

I would also assume that, if the pump needs to be set on fixed speed III and the flow is less than approx 0.2 l/s, there is something wrong. The most obvious being that the system is not correctly balanced.

However, my reason for pointing out the problem of using an ABV on anything but a fixed speed, is that it will completely mess up the flow through the system. In PP mode the ABV will open more when the flow rate increases, and vice versa; which is the opposite of what is required. In CP mode the ABV will be either permanently open or permanently closed. depending on the setting of the ABV and the chosen CP setting. As for Autoadapt, who knows what will happen!

The setting of an ABV when a modulating boiler is involved is completely different from that when a fixed output boiler is concerned.. With a fixed output boiler the flow rate through the boiler needs to be constant as the boiler output is fixed. So any reduction in flow rate, due to TRVs, MVs etc closing has to be corrected by the ABV opening. If a modulating boiler is used, any reduction in flow rate will result in an increase in flow temperature. So the boiler will modulate down to maintain the set temperature. It isn't until the boiler is running at minimum output that an ABV is necessary.

 

[John.g]

Again, I would agree with you completely but these pumps including the Alpha 2 do not provide true constant curves modes, constant curve ii at 3M has a constant head of 3M between 0 and 10 LPM, it is only when the flow rate exceeds 10 LPM that the head starts falling, in true constant curve fashion, so just as difficult IMO to set up as on constant pressure mode.
If a pump like the Dab Evosta 4-7M (a A rated pump) was installed and set to constant curve 1 at 4.2M then the head will fall to 3M for that required flow of 10 LPM and for example if a modulating gas boiler requires a minimum flow rate of 3 LPM @ 5 kw to maintain a boiler deltaT of 25C then the ABV can be set slightly lower than 3.8M, the ABV will then close once the flow rate increases above 3 LPM as the (dab) pump head will again start falling.

 

[Marck C]

Thanks 'Doitmyself' and 'John.g' for your continued comments on this topic -intriguing stuff if not a little beyond me.

I will try to comment as far as i'm able i nthe hope of filling some info gaps

1. RE ABV: it is after the pump and set at 0.3 (see pic) and there are indeed two separate valves (CH & HW) does that setting seem appropriate?
2. The BG engineer suggested it go onto setting III and as it ran quietly I thought ok fine. I did hear that setting III was to high for an open system. I'm happy to be guided on this...
3. By 'messing up flow' I'm guessing that means that the higher system pressure from setting III would 'trick' the system into diverting the heated water as it would if all the TRVs are closed. meaning that the rads wont get the heated water circulation when they are actually open and calling for it.. would that mean that the rads would not get hot? I can tell you that all the rads currently get hot.
4. RE Modulating boiler V fixed output so mine is an Alpha 18CDR is that modulating? The boiler has a manual dial type thermostat on it 1-9... I have it set at about 6.25

My other thoughts

1. The sludge on the pump rang a few alarms bells. Its an old system of pipes n rads which I'm guessing is going to be holding some sludge and crud. There is a Fernox filter on it which has been cleaned out twice since weve been here and both times it had an amount of sludge and metallic crud on it tho water from the rads on bleeding runs clear n clean. This tells me at some point we need to consider NEW RADS and a POWER FLUSH. I may well get some quotes at some point. Just don't want to mess with that right now.. I'd prefer to wait until the spring when it ain't so cold and all seems to be functioning at the mo.
2. I know the pump was fitted within the last 3 years as its date stamped at 3 yrs old... Of course i've no idea how long it had been sat on someone's shelf before fitting. No idea if the ABV setting was considered by the fitter at that point, or even if that's relevant.

hope some this helps with your thoughts on it...

Having considered all this... What pump setting would you recommend? Is there a consensus between you?

 

[John.g]

I think your boiler does modulate, probably down to 5 or 6 kw but not 100% sure.

I think you were reasonably happy a few months ago with CP1@ 3M and are now running with CP2 @4.5M, I would say either of those, whichever gives you all rads heating equally etc, my system, similar to yours runs at a 3M head equivalent, in PP mode set to 4.3M. Your system should run quite well with a 3M head if its reasonably clean.

ABV setting: I would be very surprised if your heating engineer set the ABV to 0.3 on CC iii (6M) is this would result in a huge recirculation rate of ~ 14/16 LPM, greater than your system demand which would result in a much higher boiler return temp and reducing boiler efficiency, on CP2 setting (4.5M) you would still be recirculating ~ 11 LPM with the ABV set to 0.3, I would say, based on the pump power of 35W on CP2 that the ABV is full of crap and not recirculating anything as I would have expected a power demand of ~ 42W on CP2, IF the ABV is clear and you wish to remain on CP2(4.5M) then suggest setting the ABV to 0.43 which may give you a minimum flow rate of 3 or 4 LPM. If happy to run with CP1 (3M) then set the ABV to 0.28.
If running on CP2 (4.5M) just now then the outlet pipe from the ABV should be roasting at that setting of 0.3 so adjust as required for CP2 or CP1 as appropriate.
Practically, you probably should just set it slightly higher initially and then very very gradually keep reducing the index until you just feel the by pass outlet getting hot, ie on CP2 set to 0.50 and then gradually reduce, on CP! set to 0.35 and do ditto.