Strange goings on in the bathroom

[stunlawless]

Morning everyone,

Got an usual install and weird things happening in the bathroom.

Immersion heater is switched via a contactor by the GSHP controller, which is about 30m away in an outbuilding. Contactor is in a box in the airing cupboard near the tank. Immer can also be switched by a another contactor (in the same enclosure) which is switched by a Horstman Electrisave (this setup was recommended here by Coljack IIRC).

Occasionally, a contactor can be heard to close unexpectedly. On one occasion, I've actually been in the bathroom and seen the visual indicator on the GSHP switched one showing closed. The GSHP controller shouldn't be calling for heat (it only does this once a week in the middle of the night to pastuerize the tank; this works correctly).

I've swapped the contactor with another, and the problem remains on the immer cct. Isolating the immer supply doesn't stop the contactor closing either.

The thing is, after many months I've realized that this only seems to happen in the morning. It coincides with the period that the UFH is on. The cable that supplies the UFH controller (Aube TH132) runs alongside the contactor cable for about 2m. Both are 6242Y, in 2.5 & 1.5. They are buried in the wall, which is now tiled, so are not easily accessible.

Is it possible that the UFH is inducing sufficient voltage in the contactor cable to close it ? Any suggestions on suitable datalogger (and where I can hire one) to prove or disprove my suspicions ?

If the worst is true, is there a remedy which does not involve replacing or rerouting cables ?

Thanks, David

 

[Steve]

Measure the voltage across the GSHP contactor coil when its on and off.

Have you ruled out a fault with the GSHP controller?

 

[stunlawless]

Hi Steve, No I haven't ruled out a GSHP controller fault. TBH, I'm not sure how to, given the random nature of the event.

Likewise, being there to measure voltage is a matter of luck.

I'm sure there's a datalogger out there; any ideas where I can hire one ?

Thanks, David[/quote]

 

[Steve]

When does the GSHP power up the heater? Or when CAN it power it up?

 

[LoveRocket]

There's no way that two cables installed as you say could induce enough current to energise a contactor. You problem must be elsewhere.

I have used a Fluke datalogger before at work - it was quite a hefty (and expensive!) bit of kit, so it might be overkill for your fault finding, although I know that intermediate faults are a major PITA to diagnose.

 

[stunlawless]

Steve - The only time that the GSHP controller is programmed to switch on the immer is at 0400 on saturday morning for the pasteurization cycle, and then it will use the gshp to get the dhw up to 50 before it calls for the immer. If it can't get dhw up to 50 by gshp, then it won't call for the immer , and will abort the pasteurization cycle.

Loverocket - It just seemed to much of a coincidence that a) it happens during the UFH on time, and b) the cables are under the same bit of capping. Considered opinion from here and other sources says it's incredibly unlikely, so my thoughts are turning to the GSHP controller having some "unspecified functionality".

I guessed any suitable kit would be pricey, that's why I though about hiring one. Any ideas where to look ?

All thoughts gratefully recieved, David

 

[Lectrician]

Even hiring them is at least £100.

We use a company called ELcomponent.

 

[stunlawless]

Hallo Lectrician - I looked into hiring last night, and it scared me...could quite easily run a bill of several hundred to try to find & fix an intermittent fault, so I'm going to fall back on the five senses !

Thanks, David

 

[LoveRocket]

I've re-read your post again, and it does sound like an intriguing problem.

These two contactors, are they wired parallel with each other, ie the supply splits off to each of them before the load sides are combined again to the immersion? Or does the Electrisave switch a supply to the coil on the main one? (I ie the coil on the main one is supplied from both the GSHP controller AND the other contactor)

When you see this contactor closed, can you check on the GSHP controller if it's calling for the immersion?

Is the UFH electric (sorry if that's a daft question, I've never worked with it before)?

 

[stunlawless]

Hallo Loverocket,

These two contactors, are they wired parallel with each other, ie the supply splits off to each of them before the load sides are combined again to the immersion?

Yes, spot on. I discussed this here before, and considered opinion was that it was a good solution to switching one heater from two controllers.

Very difficult to see if the GSHP controller is calling for heat when the contactor closes. GSHP is another building, so it means running across the yard when you hear the clunk, and ideally another observer watching the contactor and both being in contact by phone ! I've never achieved it yet !

I've thought about how to datalog the output from GSHP, and it looks like costing ~£100/week for a suitable bit of kit, so I'm thinking of other ways to do it.

The UFH is electric. I've discounted any influence from the UFH, as my wife confessed that she'd heard the "clunk" at random times through out the day, not just when the UFH is on.

One thing I did discover last night is that contactors should not be installed adjacent to each other - there should be a space between them. Hager have said this is to prevent overheating, but I've removed the electrisaver one & connected all the cables to the earth bar, just to try to eliminate any possibility of interference. Schoolboy error; should have read the MI's !

I'm now thinking that it's either interference/backfeed from the cable installation, or "unspecified functionality" in the GSHP controller, though I don't know how I'm going to measure anything.

I've thought about how to datalog the output from GSHP, and it looks like costing ~£100/week for a suitable bit of kit, so I'm thinking of other ways to do it.

Maybe there's a way with installing neons across the wires, but it still needs someone to see it.

Any thoughts are most welcome.

Thanks, David

 

[madmole]

A lot of multimeters with RS232 interfaces come with datalogging software that runs on your laptop. Can get this functionality for sub £59 at Maplins

 

[stunlawless]

Hallo madmole,

Brilliant ! There I was, scaring myself at Fluke & Megger prices, when you point out the way I should be thinking.

Just bought a Chinese one from Maplins for £50 all in.

Thanks for bringing me back to earth, David

 

[electronicsuk]

Do let us know how you get on, although I'm not sure what you intend to prove using the logger? As already mentioned, there's not a cats chance in hell that the two cables running parallel could be inducing enough current to bring the contactor in. Either the wiring is incorrect, or the coil is being energised because the ground source heat pump IS calling for it, for reasons unknown. Perhaps if it aborts the cycle, it will try again and again until it's able to heat the tank to 50 degrees?

 

[stunlawless]

Breaking news: heard the "clunk" this morning, so removing 2nd contactor has no effect. After discussion here & with Hager, I didn't really expect any different, but it's good to have another possibility discounted.

When I get the logger set up, I intend recording voltage at different points and trying to correlate it with observed clunks. Ideally, I'd have a multichannel set up, but that isn't gonna happen.

I will keep you updated but it will be a little while until I've got some data and conclusions.

Thanks, David