My GSHP trips 32A MCB

[nowty]

Every time I put a new fuse in it starts ok for a few days before it goes and it seems to go when its not been used for a while, like overnight. I've tested the contactor and I'm sure its OK. No sign of any sticking and the contacts reads zero ohms when its energised.

There is a possibility its just aging and I need a higher fuse rating than 13A. I have a feeling it did blow a fuse once before a long time ago. The fuse size was just what I thought it should take rather than what the manual says. The manual does not say anything, another badly translated chinese one.

Anyways I am off to my folks tomorrow so cannot look at it again till next week. SWMBO is holding the fort but so far looks like almost normal temps are being maintained with the A2A HPs and storage heaters even at these constant sub zero temps. Might have to leave the HPs on 24/7 though.

[Oldgreybeard]

I'l llay money it's not unloading fast enough after a stop. Pretty common problem with fixed speed heat pump compressors, lots of stuff on the internet about unloader valves.

[marshman]

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[Oliver90owner]

Unless there is/are other load(s) on that circuit, I would suggest that a 13A fuse is not the correct value for a 32A circuit breaker.

Does it both trip the MCB and blow the fuse? What power is the motor?

Most compressor circuits have a thermal trip to protect against too-early restarts - well every fridge and freezer I have owned have worked that way. If the motor is in a stall situation, it will likely draw rather more than 3 times its normal running current.

Is it a direct or belt drive from the motor to compressor?

[nowty]

Unless there is/are other load(s) on that circuit, I would suggest that a 13A fuse is not the correct value for a 32A circuit breaker.

Does it both trip the MCB and blow the fuse? What power is the motor?

Most compressor circuits have a thermal trip to protect against too-early restarts - well every fridge and freezer I have owned have worked that way. If the motor is in a stall situation, it will likely draw rather more than 3 times its normal running current.

Is it a direct or belt drive from the motor to compressor?

It occasionally blows the 13A local fuse but not the 16A breaker.

The thread was started a year ago with a different failure which I fixed. Its now on a 16A breaker shared with my other lower powered A2A HP. I'll probably split them off onto separate breakers next year. I was not expecting them to run together and they generally don't but even when they do the MCB does not go even though the 13A local fuse does.

The 16A MCB vibrates for about 2 seconds when the compressor starts but I witnessed the fuse blowing and the vibration from the MCB went on for about 4 seconds.

The compressor is a small rotary direct drive unit, power starts about 1.5kW and goes up to a little over 2kW as the temp increases. That includes the water pumps.

[Oldgreybeard]

A 16A B curve MCB has a much slower time/current curve than a 13 A fuse.

I still very strongly suspect this is just an unloader valve issue, most probably related to a slow leak back from the HP side when the unit is cycling a little bit too fast, as it may well do in cold weather.

[nowty]

I think I've fixed the latest problem at least for now.

I have done two things,

1) Increased the local fuse size from 13A to 20A, its still on a circuit protected with a 16A MCB.

2) I removed and gave the main compressor start up contactor a jolly good thrashing and workout.

Since doing this its worked fine, not only fine but when it starts the 16A MCB no longer rattles at all. I've tried running it on a long cycle and leaving it and I've tested it on a short cycle time with immediate restart although there is a 2 min delay built in.

So my suspicion is the contactor, maybe not latching properly or a bit of grit in there. The HP does not get used for Summer as no need for heat and the hot water is from the solar diverters. I noticed this MCB rattling when it came back into service but I just assumed it had always done that.

Another contactor is on the slow boat from China, so for now I will just see how it goes. If it does turn out to be the contactor and it reoccurs at least I will have a replacement.

[Oldgreybeard]

Not unknown for Chinese made contactors to fail. Our Sunamp control box was first delivered with a 20A rated DIN contactor of unknown parentage, failed within a couple of months (and was a bit noisy before that). It was replaced under warranty and the replacement went the same way (and was also noisy before it failed). I fitted an ABB one and that was silent and has been 100% reliable.

I think there may be a parallel with the cheap RCBOs that Rolec were fitting to their chargers years ago. They came from some unknown source in the Far East and failed with monotonous regularity. People that replaced them with brand name units found the problems went away.

[nowty]

Update on my latest GSHP problem and I think its now fixed.

The HP ran OK for about a week but blew the fuse again at the higher 20A rating. My replacement contactor arrived from China so I changed it over and have not had a problem again in 6 weeks operation so I think the problem was either a slow acting contactor (to the main compressor) or the contacts had become damaged.

The other good thing is after finding a burnt out loose connector over a year ago which was killing my water pumps, I have not had a single failure since.