Grundfos pump having a microsoft moment

[bungeejumper]

One for the plumbers, I think? I've searched the web for this prob, but would be really grateful for any thoughts.

Our central heating system has a Grundfos Alpha 2L pump, one of those all-singing eco-friendly types where the speed and flow are dynamically controlled by a chip that automatically decides how much electricity to use. It's about five years old, and we quite like it because it's smooth and quiet. But last night it failed to come on.

Oh, the boiler fired up okay, but the rads stayed cold. Upon closer inspection, the main power light on the pump was on, but it hadn't selected a speed, and the manual selector buttons were non-operational. I earned some brownie points from SWMBO with a quick Microsoft fix (turn the power off at the connector box and turn it on again), and we were up and running in moments. But I'd prefer to know why it threw the wobbly in the first place. The thought of a massive great Rayburn boiler firing up when the pump wasn't working could give me sleepless nights! (The water in the pipes around the boiler was boiling and bubbling up nicely. )

Is this just something that happens with these electro-clever pumps - a transient throwing them out, perhaps? Could it signify a prob with the motorised valve next door? (Seems unlikely.) Could it be due to stirred-up crud in the system? (I had added a couple of litres of inhibitor and anti-kettling agent to the header tank a couple of days earlier.) Or is it an early sign of pump failure?

Thoughts?

TIA, BJ

[Itsallaguess]

One for the plumbers, I think? I've searched the web for this prob, but would be really grateful for any thoughts.

Our central heating system has a Grundfos Alpha 2L pump, one of those all-singing eco-friendly types where the speed and flow are dynamically controlled by a chip that automatically decides how much electricity to use. It's about five years old, and we quite like it because it's smooth and quiet. But last night it failed to come on.

Oh, the boiler fired up okay, but the rads stayed cold. Upon closer inspection, the main power light on the pump was on, but it hadn't selected a speed, and the manual selector buttons were non-operational. I earned some brownie points from SWMBO with a quick Microsoft fix (turn the power off at the connector box and turn it on again), and we were up and running in moments. But I'd prefer to know why it threw the wobbly in the first place. The thought of a massive great Rayburn boiler firing up when the pump wasn't working could give me sleepless nights! (The water in the pipes around the boiler was boiling and bubbling up nicely. )

Is this just something that happens with these electro-clever pumps - a transient throwing them out, perhaps? Could it signify a prob with the motorised valve next door? (Seems unlikely.) Could it be due to stirred-up crud in the system? (I had added a couple of litres of inhibitor and anti-kettling agent to the header tank a couple of days earlier.) Or is it an early sign of pump failure?

Thoughts?

The manual for the Aplha 2L pump suggests that those symptoms could be a power supply issue or a pump blockage -



GRUNDFOS ALPHA 2L (PDF Manual) - https://api.grundfos.com/literature/Grundfosliterature-1191164.pdf

The mention of a potential blockage issue on the above manual snapshot, aligned with your recent addition of treatment to the system does make you wonder if they're related...

As an aside, it's always worth checking the line-up of motorised valves on central-heating systems, just so you know what 'normal running' looks like in various states (hot-water only / central-heating / zonal line-ups etc..), so that when these types of issues do occur, at least those valve line-ups can be quickly checked to see if they might be related...

It's certainly worth doing that if you can get the system working for any length of time, and if this turns into a more persistent problem with the pump.

To be honest, my main worry would be with you mentioning local boiling when the pump wasn't running and the boiler was still firing. There should be a local boiler-stat that prevents that issue, so that aspect seems to me to be the most concerning, to be honest...

If the system is easy to drain and re-fill, then that might be the route of least-resistance to at least rule out crud in the pump, but given the recent treatment, it might settle down soon again anyway...

Cheers,

Itsallaguess

[Mike4]

To be honest, my main worry would be with you mentioning local boiling when the pump wasn't running and the boiler was still firing. There should be a local boiler-stat that prevents that issue, so that aspect seems to me to be the most concerning, to be honest...

This was the 'stand-out' issue in the OP for me too. Assuming the Rayburn is solid fuel it is classed as an "uncontrolled heat source" and should have a decent sized radiator connected so as to operate by natural convection as a "heat leak" to stop the thing boiling should the pump fail.

If the Rayburn is oil or gas fired, it sounds to me as though both the control thermostat and the overheat thermostat have failed or lost their calibration.

Getting back to the Grunny, IAAG is probably right about some crud blocking it. The other possibility with Grunny electronic pumps is the early models suffered failure of the speed sensor, leading to the pump running for about 1/10th of a second then resting for 9/10s of a second. This failure mode is not documented anywhere I've seen, but was quite common about five years ago and caused me a great deal of grief.

[bungeejumper]

Thanks for all those thoughts, Mike4 and IAAG. Plenty there to think about. And yes, the crud theory does seem to fit the situation best. It's not a huge faff to drain the system and strip down the pump impeller - a couple of hours at most. We're at home pretty much 24/7 so I'll watch it for a week or two and see where it goes.

WRT the Rayburn (which is "blown gas", BTW), it does have an integral thermostat, which was switching in and out yesterday as it should. But half a tonne of cast iron behaves a bit differently from the usual skinny steel boiler box, and you can find that it retains localised high heat in ways and places that wouldn't make sense to a conventional boiler engineer. Like turning a supertanker round, there are long time lags behind doing stuff and seeing the results. (Which is why it isn't normal to use a room stat with a Rayburn - it would always be half an hour wrong!)

They don't make blown gas boilers for domestic purposes any more - only for manufacturing industries. But you can still buy a half-tonne cast iron Aga or Rayburn with a vertical flue for your kitchen, because the EU flue regulations have been specially bent to accommodate any boiler that can also realistically be described as a cooker. It's a funny old world.

Thx again!

BJ

[Mike4]

Thanks for all those thoughts, Mike4 and IAAG. Plenty there to think about. And yes, the crud theory does seem to fit the situation best. It's not a huge faff to drain the system and strip down the pump impeller - a couple of hours at most.

BJ

Do you not have isolation valves either side of the pump? If you have and they work, close them. Then you don't need to drain down.

[bungeejumper]

Do you not have isolation valves either side of the pump? If you have and they work, close them. Then you don't need to drain down.

We do, and they do, and I can. But that wouldn't clean the system of crud, I suspect?

Mind you, I shall weep for the loss of about £100 worth of additives if I have to pour it all into a bucket. It's a 200 litre system, with very hard tap water, and there's four litres of X200 in there now, plus two litres of X100.

BJ

[Mike4]

Do you not have isolation valves either side of the pump? If you have and they work, close them. Then you don't need to drain down.

We do, and they do, and I can. But that wouldn't clean the system of crud, I suspect?

Mind you, I shall weep for the loss of about £100 worth of additives if I have to pour it all into a bucket. It's a 200 litre system, with very hard tap water, and there's four litres of X200 in there now, plus two litres of X100.

BJ

Oh I misunderstood. I thought you meant clean the crud from the pump impeller.

With a bit of ingenuity (involving say, a couple of plastic dustbins) you could catch the water then put it back in again, after you have flushed the system....

On the other hand maybe there is no point, given the suspected ineffectiveness of the Sentinel!

[bungeejumper]

Oh I misunderstood. I thought you meant clean the crud from the pump impeller.

Oh, I'll do the impeller as well, fear not.

With a bit of ingenuity (involving say, a couple of plastic dustbins) you could catch the water then put it back in again, after you have flushed the system....

Genius idea. Then all I have to do is carry 200 kg of strained but mucky water up a ladder, to get it up into the roof space (about 45 feet), so that I can tip it back into the tank.

(Seriously, I did once do that with about 100 litres. Which was a useful whole-body workout, and quite hard on the nerves. I was still aching the following week! ) These things are sent to try us. It's odd how they succeed, isn't it?

Anyway, boiler and pump are behaving themselves nicely at the moment. Here's hoping the bumpy patch has sorted itself out. I'd rather be draining down in summer than in mid-winter, that's for sure.

BJ

[Mike4]

Genius idea. Then all I have to do is carry 200 kg of strained but mucky water up a ladder, to get it up into the roof space (about 45 feet), so that I can tip it back into the tank.

I know!

And there was me imagining rigging up a hose pipe and a pump of some sort.....

[jfgw]

I have repressurised a system with a test pump. Completely filling a large system with one of those might take a while, however.

You would need a pump with sufficient head so borrowing the one from the pond probably won't work, nor would pouring the manky water into the washing-machine while the wife is out and extending the discharge hose into the loft.

Julian F. G. W.

[bungeejumper]

You would need a pump with sufficient head so borrowing the one from the pond probably won't work, nor would pouring the manky water into the washing-machine while the wife is out and extending the discharge hose into the loft.

Thanks for the laughs, both. But still, it might work if I perhaps hoisted the washing machine into a nearby tree?

BJ

[DrFfybes]

Oh I misunderstood. I thought you meant clean the crud from the pump impeller.

Oh, I'll do the impeller as well, fear not.

With a bit of ingenuity (involving say, a couple of plastic dustbins) you could catch the water then put it back in again, after you have flushed the system....

Genius idea. Then all I have to do is carry 200 kg of strained but mucky water up a ladder, to get it up into the roof space (about 45 feet), so that I can tip it back into the tank.
BJ

That's a bit excessive. If you have a towel rail all you need is a step ladder, a jug, and a funnel

If not one of these is a lot of money for what it is, but well worth it if the installer has wedged the F&E tank so high in the eaves you can barely get your hand i th top of it.
https://www.screwfix.com/p/flomasta-uni ... -pcs/8145k

Paul

[bungeejumper]

Swift follow-up. So far, so good, everything behaving itself, so maybe it was a one-off. The top tank wasn't that mucky actually - I'd drained and cleaned it about three years ago, and any deposits in there seemed to be soft. But it's still on my agenda for the spring.

It'll be a relief not to have to drag my washing machine up a tree. Although (slaps head) my pressure washer would be well capable of pumping to loft height. It cleans the gutters, after all.

Thanks again

BJ