Fireman switch failure?

insular1 · 02-03-2026 12:24PM #1

Hi all,

This morning I heard a sound like a whirring followed by a loud click from my solar system. It reminded me of the noise the fireman switch makes when you turn off the panels at the DC isolator but was louder than usual, and it never normally happens unless I manually switch the panel DC isolator.

After the sun came up, the system seemed to be working fine. The panels were producing up until about 10:20, and then, all of a sudden, even though there was still plenty of sun, production dropped to zero. Inverter still working supplying the house from the battery.

I wasn’t home when it happened, so I didn’t hear if there was any click or noise from the fireman switch at that time.

It’s weird because the loud click happened before the sun came up (which I noticed), then the panels started producing normally, and only failed after a couple of hours of production.

If it is the fireman switch, are they easy to replace? Can any electrician handle it, or would you need a solar specialist? Is it something that can be safely DIY’d? Are fireman switches even strictly necessary, could I simply remove it or get the electrician to do it?

graememk · 02-03-2026 01:28PM

https://www.boards.ie/discussion/2058434829/fireman-switch-failure

Could the rcbo of the inverter be also tripped as usually the fireman switch is connected to that

Edit, I've just read the rest of your message...

Try cycling the power to it

insular1 · 02-03-2026 01:59PM

I'll try a power cycle when I get home tonight and feedback the results. Hopefully be home while there is still some sun to test it with!

graememk · 02-03-2026 02:10PM

There should be a isolator switch for it beside the inverter, means you don't have to turn everything off

insular1 · 02-03-2026 06:01PM

Went home early to try and troubleshooting and went to power cycle the panels and noticed they were back producing. Started back about an hour ago. No errors on the inverter no hint as to why it stopped at all. Hopefully just some random glitch. As they've been working flawlessly for years. I'll monitor closely over the next few days and see.

insular1 · 03-03-2026 12:47PM

Happened again today. Unfortunately in work so can see what happened. All of a sudden despite plenty of sun 10:30 similar time to yesterday, panels stopped producing. Then about an hour later they started producing again, but just as I was typing this they stopped. I have attached a chart of PV power from solar assistant. Red arrows are where it stops abruptly and green where it started back again. Any ideas what could cause this? Faulty fireman switch?

image001.png

JIdontknow · 03-03-2026 01:03PM

Is it the exact time of day it’s happening and the downtime the same, just wondering Is there a pattern there, is it cyclical?

insular1 · 03-03-2026 01:49PM

Hadn't thought of that. Went down at exactly 10:23 yesterday and 10:17 today. Very similar time. Could be related to the amount of solar being produced at the time? Both days equally sunny and both times just before it shut down it had been producing just under 2kW. So possibly the time, or the current causing something to trip?

graememk · 03-03-2026 02:14PM

https://www.boards.ie/discussion/comment/124280982#Comment_124280982

Check the DC isolator too (but when it's dark). Something is dying. When my dad's isolator burned out (it was outside, it absolutely stank)

Should be a simple swap out for either device

insular1 · 03-03-2026 02:19PM

Thanks. I'll get onto my electrician and see if he'd be happy to do it, but he's not a solar installer so might not be comfortable. I thought I read somewhere after I got my installation done that fireman switches are no longer required. Is this true? If so can I just get the electrician to take it out and have the system run without it?

graememk · 03-03-2026 09:43PM

As far as I know the fireman switches are in the regs now. they originally were just seai requirement/advisement but its in the rules now.

insular1 · 07-03-2026 12:45PM

Just to update this in case anyone else has a similar issue. I got into the attic to have a look at the fireman switch on Tuesday once the sun went down, it's a projoy and was a much simpler device than I had in my head for some reason. Isolated the AC and DC and bypassed the switch simply plugging in the correct MC4 connectors together. Then we had hardly any sun for a couple of days so couldn't see if it had made a difference but yesterday the system was back producing as expected, definitely the fireman's switch. Have ordered a replacement and will fit myself, looks at about the same level of difficulty as wiring a plug, all the DC side is plug and play MC4. Thanks all for the help.

SD_DRACULA · 07-03-2026 11:03PM

https://www.boards.ie/discussion/comment/124293361#Comment_124293361

Had something similar happen a while back and I re-did the AC connections on the projoy and it all came back to life and has been working since. Check that first.

insular1 · 08-03-2026 10:25AM

I'll give it a go. Have already ordered the replacement but can keep that as back up if I can get the old one working. From reading around it's likely to fail at some point anyway and it's been running for around 6 years now without issue.

DC999 · 09-03-2026 11:03AM

https://www.boards.ie/discussion/comment/124295536#Comment_124295536

I think the Projoy have a 7 year warranty from memory. Mine died after 2 years and I checked at the time. My installer replaced for free.

Fireman switch failure?

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