My GSHP trips 32A MCB

[Bugtownboy]

Nowty, and I apologise if this is a stupid suggestion (I’m a, let’s say life scientist) but could you create a micro environment around the pumps with the heated water to get them above dew point ?

If I understand your set up, would it require some minor reconfig and a ‘boxed’ isolated, but ventilated, area ?

Please don’t shout if I’m barking up the wrong thing

[nowty]

Nowty, and I apologise if this is a stupid suggestion (I’m a, let’s say life scientist) but could you create a micro environment around the pumps with the heated water to get them above dew point ?

If I understand your set up, would it require some minor reconfig and a ‘boxed’ isolated, but ventilated, area ?

Please don’t shout if I’m barking up the wrong thing

There is no such thing as a stupid question.

I sort of already have made a micro environment for them, my insulation on them stops most of the condensation as it reduces the amount of damp air finding its way to the cold pump surface and I think my towel bandana may help further. If it does not, then I'll buy a more expensive pump to eliminate the problem. I see the water pumps as cheap consumable items and this recent problem would have been a 15 min fix if I had not gone down several other blind alleys. I'd just never had this symptom of a tripped MCB before so it convinced me there was a far worse problem.

This is a view of the water pumps (only 3 in this picture) when I was testing out the heat pump back in 2018, the two black water pumps at the back are the cold circuit ones.




Each pump has a layer of polypropylene covering them.




Then there is another thermal jacket covering them with cable ties to hold the jacket in place. Finally the towel bandana around the pump at the bottom of the thermal jacket is my latest modification.

[AE-NMidlands]

I am afraid there is a problem with the usual understanding of humidity and condensation.
A psychrometric chart https://www.engrsuccess.com/engineering ... ric-chart/ helps - but this one doesn't have what I'm sure the ones I used to use had: a vertical scale on the RH axis showing mass of water per unit volume of air (corrected for temperature.) Maybe you can get it by working back from what they do show, but it is a big loss for those of us not designing A/C systems in hot humid environments.

The point is that cold (0 degrees C) air has almost no moisture-holding capacity, but at 10 degrees it is massively higher. Thus, if air at 10 degC passes over a pipe at 4 or 5 degrees you will almost certainly get condensation, and it will get much worse with every degree below that.

So I would guess that even pipes and pumps carrying well water at 4 or even 8 deg C will attract loads of condensation if a) outside air can circulate over them and b) the ambient air temp is anything like 10, let alone higher.
A

[nowty]

Even though a few weeks back I found the burnt out electronics board in the failed water pump, something just did not seem right and it has been troubling me ever since. Why did it randomly cause a 32A and even a 63A circuit breaker to occasionally trip and not the RCD. A couple of you said a similar thing. Other previous failed water pumps did not trip out anything. I was just happy that the thing was running ok again but I don't like it if I cannot explain what happened.

But now I have found the REAL problem with the MCB tripping, the failed water pump was probably a symptom of the real problem.

The heat pump tripped the 32A MCB again this morning with the same water pump failure. Hmmmmmm, well I swapped the pump out again and the new pump was all over the place, but generally LED flashing, pump restarting again, LED flashing again. Depending on the interval of flashing tells you what's wrong but it was sort of random flashing.

I gave the mains connector to it a waggle and heard a fizzing sound. OK, sounds like the connectors loose, so back in the house to trip the MCB myself but found the whole house off as the upstream 63A breaker had tripped as well as the 32A breaker.

Took the connector apart and found this,



Its about the worst designed plug I have ever seen in my life, the wires are held in place with a very weak spring. The wires actually go in the other side to the photo and have to be bent 90 degrees to get them into the holes, but a lot of the time the spring does not hold them and they pop out. After much faffing and a fair bit of swearing, managed to get them in and funny enough the water pump now works. Hopefully the one I removed this morning probably works too.

Checked the other 3 connectors and they are still OK, so now I am happy in my own head that everything that happened is now fully explained, especially why the RCD did not go as it was just the live and neutral in the connector shorting out. And also explains why I checked the water pumps after the first trip out and I was sure all 4 water pumps were working. The intermittent supply to the water pump probably caused it to fully fail a week later.

[spread-tee]

Ahh, that's more like it, I didn't think that pump PCB looked burned enough to trip a 63 amp breaker. I'm glad you found the real culprit, it is a horrible nagging feeling not being sure you have sussed a particular issue especially with a safety critical issue like this.

Phew

Desp

[Tinbum]

Possibly condensation has caused it to arc between the two terminals and carbonised the plastic to then become an even better conductor.

[AE-NMidlands]

Will you be replacing the connectors with something more fit-for-pupose (i.e damp-proof?) Or is it not possible to get the other bit off the pump?
A

[nowty]

I think it was more of a loose connection than condensation and the other 3 looked ok, but in one of them the wires came out with the lightest of pull with my fingernail so I re-terminated that one. They are just a terrible design and no chance of replacing them with anything else as the plug and socket connectors seem very bespoke.

But now I know the issue, its something something easy to keep an eye on.

Next summer I might connect each water pump up to a wall mounted bank of 6A circuit breakers which I thought about doing when I installed it but then thought, nah.

[nowty]

Another year on and another intermittent problem has arisen with my ground source heatpump. Not my recent A2A HP's, there are doing the business.

This time, instead of the circuit breaker tripping and the local 13A fuse staying intact, the 13A local fuse is occasionally blowing on starting but the circuit breakers stay put. It was happening about once a week and now its once every 2 or 3 days.

Tried the usual suspects, the water pumps but they are fine and I've checked the connectors to them and they are all fine.

I eventually managed to catch the fuse blowing and its definitely happening when the main compressor starts. So tested the starting capacitor, but that checked out at almost the same 49uF as last time (Its badged a 50uF).

So all I'm left with is either a knackered compressor, but once its running, its fine, so my next suspect is the contactor for the compressor. No loose connections, but maybe its failing. Took it out and it does not smell burnt.

I'm going to test it but I can get a replacement from china for £15 including postage so I've ordered one just in case as it might take a few weeks.

In the meantime my A2A HPs are heating the house in conjunction with my the storage heaters. For hot water I will rely on the twin immersions which will add a few extra kWh but I am still not resorting to the gas boiler yet.

[Oldgreybeard]

Does the unit have a compressor unloader valve? Sometimes a high pressure on that side on startup can create a higher load and therefore cause the start current to rise. Ignore this if the unit has a VFD and a three phase motor driven by that, it's only an issue for direct drive, capacitor start, compressors (which it seems yours may be). The HP side is unloaded either by an an electromagnetic unloader valve, or sometimes by a bleed back that takes time to reduce the HP side pressure, It's possible that too frequent starts in this cold weather might mean there is insufficient time for the latter system to unload the HP side before the next start.

As a test, try leaving the unit off for, say, half an hour or so, then trying it again. If it starts up without issue then that tends to point to the pressure on the HP side at start being the possible cause.

Some systems unload by allow the HP side to connect to the LP side, does the same thing, takes the load off the compressor scroll/piston(s) at start up, so the starting current is reduced.