Hot water tank is boiling over. Scolding hot showers.

TomArch · 18-07-2023 07:39AM #1

Hi, I'm hoping someone can help me.

I have a direct hot water cylinder setup that's connected to a hot water tank above. I don't have a boiler and rely on the immersion for heating.

My storage tank will heat up on off-peak hours for me to use in the day.

I don't have central heating, the cylinder is solely for the shower (my bathroom/kitchen taps stopped heating up a year ago, I presume it's an unrelated issue).

I've woken up at 3am to when my hot water is heating up to the pipes shaking violently and the hot water tank is bubbling and boiling over.

When I turn off the heating the boiling will stop within 10 seconds.

I just had my cylinder replaced and these issues started two days afterwards.

The plumber who installed it has replaced the immersion as he deemed it faulty, however it hasn't fixed the issue at all. He's now not sure what to try next.

I was hoping that someone here may have a suggestion. I've read through several forums here but none of them appear to have the same setup without a boiler/with a hot water tank.

Sorry about the rotated photos, can't seem to fix that from my phone.

Thank you,

Tom

Calahonda52 · 18-07-2023 07:55AM

thermostat in the immersion is goosed, its in the black thing on top of tank in second last photo

not a big deal to fix but best left to a sparks

TomArch · 18-07-2023 08:10AM

Thank you for the quick response.

What do you mean by goosed? I've already had the thermostat fully replaced and the issue still arrises.

carveone · 18-07-2023 08:19AM

I'd be surprised if someone went to the trouble of replacing the immersion and not the stat. The latter is a 5 min job. First thing I thought of was the stat; they do fail and many of them have no secondary overheat safety. Cue a boiling cylinder. Which can deform your tank through the expansion so might want to watch that...

TomArch · 18-07-2023 09:53AM

Hi, I can confirm that the stat was replaced yesterday. Both stats were brand new.

I'm keeping it all turned off until I know what I can do to fix it.

zg3409 · 18-07-2023 10:08AM

It may be wired up wrong. Plumbers are not the best electricians. Chase plumber to fix the issue.

Furze99 · 18-07-2023 10:24AM

I'd think the black plastic tank above your cylinder is cold water storage, not hot water as per OP. As you draw off hot water from cylinder, it's replaced by cold water from that tank. That's how it looks anyway.

As for overheating water, has to be the thermostat on immersion if you've described correctly or how it's wired. Apart from danger, heating water like that tends to be expensive.

Calahonda52 · 18-07-2023 10:44AM

turn off the power to the immersion

make sure power is off

take off the black cover and see what the stat is set at: pls post a picture

https://www.reddit.com/r/Plumbing/comments/f8am12/immersion_heater_help_please/

should be at around 60

Citizen Six · 18-07-2023 10:51AM

https://www.boards.ie/discussion/comment/120865557#Comment_120865557

How come your plumber can't figure out what the issue is? Is he a qualified plumber, or some kind of handyman?

Probably best off with an electrician and a plumber to test everything, as it seems like it's probably wired incorrectly if the stat was replaced and the same issue is still there.

You saying you have a hot water storage tank sounds a bit odd. I presume you mean the black tank above, but are you expecting it to store hot water for you?

How come you don't have hot water in any of the other taps?

If you only need water for a shower, you'd probably be better off with an instant shower, rather than heating a cylinder like that.

18-07-2023 10:58AM

https://www.boards.ie/discussion/comment/120865786#Comment_120865786

This. ^^^

Get a better plumber, one that is competent to liaise with and engage other trades as required.

carveone · 18-07-2023 11:32AM

https://www.boards.ie/discussion/comment/120865754#Comment_120865754

I was reluctant to suggest that on the grounds that if it was wired wrong (which boggles the mind frankly) then god only knows what's going on. For all I know the switch is on the neutral and we'd end up with a fried boardsie.

spaceHopper · 18-07-2023 11:34AM

Either the thermostat is set to max or it's not working. You could shut down the power and see if you can adjust it or you could change the timer so that the water is on for a shorter time, that would give you some hot water. Start with half an hour and go up to 45 minutes. Be careful that if are away then the water isn't used so over a few days it could get very hot.

TomArch · 18-07-2023 12:15PM

Thank you all for the help. To answer some questions:

The stat is definitely set to 60. Both the new one and old one were. I guess it's possible but unlikely that both are faulty?

My plumber advised that the black tank above the cylinder is a hot water storage tank. My system is setup so that it heats water on off-peak times which I can then use throughout the day. The black tank was what was boiling and bubbling so if it's cold water storage then something's definitely going wrong.

My plumber did say many times that the setup is very unprofessional and he can't figure out why the last guy piped my system the way it is...

My plumber has now advised he thinks it may be the element on the immersion, or unlikely an electrical surge (I have a switch fuse in place so I don't think so). I don't know if I'll go forwards with this or not

Thank you all again, this is very helpful.

TheBigLebowski · 18-07-2023 12:22PM

Do you live in a hard water area? Do you get limescale in your kettle, etc?

TomArch · 18-07-2023 12:22PM

Oh, and my timer is fixed. I can't change the range of hours it'll turn on for, just the time of day. It'll always be on for 3 hours twice a day.

10-10-20 · 18-07-2023 12:34PM

https://www.boards.ie/discussion/comment/120866164#Comment_120866164

Eh, that looks wrong to me. The stat needs to be in-circuit with the element and it looks like it's sitting partially connected. Can you photograph the other side of the element wiring showing where the farthest white wire to the stat is?

carveone · 18-07-2023 12:45PM

https://www.boards.ie/discussion/comment/120866218#Comment_120866218

That's definitely wrong. The immersion is clearly wired straight to the mains.

This is shockingly (sorry) bad. The way it's supposed to be is that the neutral goes to one side of the element and the live goes through the stat to the other side. The stat is a switch - whoever wired that doesn't know what a switch does.

10-10-20 · 18-07-2023 12:47PM

https://www.boards.ie/discussion/comment/120866274#Comment_120866274

Exactly! I'm just hoping that it's not wired as a direct short across the element! I'm presuming not, but best get the photo to check!

Spear · 18-07-2023 12:52PM

This has nothing to do with boards.ie. Moved to a forum that's related to the topic instead.

cfingers · 18-07-2023 12:55PM

https://www.boards.ie/discussion/comment/120866274#Comment_120866274

Was just about to say that. So the stat is completly bypassed and not serving any function.

The immerison tank is over heating and thefore water going into overflow into the cold water tank (black tank). The hot water hitting the cold water is causing the bubbling.

Get an electrican( or af least someone that knows what they are doing ) to wire it correctly.

eurokev · 18-07-2023 12:56PM

It looks like your plumber has wired directly in to the element bypassing the thermostat.

The brown core should be on the other side of the thermostat. Electricity then comes in on your brown wire, through your blue thermostat and on to the heating element via the white wire.

From the picture the brown wire is connected directly to the white wire. This takes the thermostat out of the circuit. The thermostat acts like a switch which turns off when the temperature in the tank gets above 60degC.

I am pretty sure this is the problem. Post another couple of pictures to confirm.

If this is the case, make sure you never get that plumber to do work for you ever again

eggy81 · 18-07-2023 01:04PM

https://www.boards.ie/discussion/comment/120866286#Comment_120866286

It’s wired straight across the element judging by that pic. Wouldn’t be a short as the resistance of the element is in circuit. Op take the brown off the element pole and connect to far side terminal of stat and it should fix problem. Your stat is bypassed altogether in that pic. Obviously kill power first. Seems a highly unorthodox system you’re running there.

10-10-20 · 18-07-2023 01:15PM

https://www.boards.ie/discussion/comment/120866357#Comment_120866357

You're confusing series and parallel. If the element and stat were wired in series (one after the other) then we would not be having this issue and the resistance of the circuit would be effectively the resistance of the element and stat added together (and all would work fine). In parallel the resistance of the circuit would be 0 ohms as the stat has almost no resistance and the resistance of the element would be ignored.

Anyway, it will be interesting to see what's happening on the opposite side of the stat.

TomArch · 18-07-2023 06:40PM

I don't know much about wiring but here are pics from all angles. I also think the previous pic was the previous stat before it was replaced.

Do you all think that I shouldn't get the plumber back out and instead get an electrician?

Fyi you've all been incredibly helpful and eye-opening. Really appreciate all the comments.

eggy81 · 18-07-2023 06:59PM

Take brown off the place it currently is and put it into the connection hole/ terminal you see on the near side of the stat in the first picture of these 4. Stat is currently bypassed/not in the circuit. No way of switching off when temp is reached

bmc58 · 18-07-2023 07:02PM

https://www.boards.ie/discussion/comment/120865245#Comment_120865245

Neds to be replaced.

Wearb · 18-07-2023 07:15PM

Whoever you are getting to do it, don't let the last guy within a mile of any electrics.

Windowsnut · 18-07-2023 07:17PM

If you don't fix that fast, the boiling hot water will melt the seals on the pump and it will start leaking - it happened in an apartment a friend of mine was renting out - a pinhole leak developed and destroyed the place.

The pump seals are rated for 60 degrees Celsius, I set my immersion thermostat to 50 degrees (10 degrees below the rated temperature of the seal.)

Wearb · 18-07-2023 07:20PM

Pump seals are the least of your worry. There has been at least one death caused by the plastic expansion tank loosing its shape and spilling over boiling water through a ceiling onto a sleeping occupant.

John.G · 18-07-2023 07:24PM

Just do as suggested above, remove the brown wire and place it in the stat terminal near where "240V" is written on the stat, you will then have live through the stat and through the element and back to the consumer unit/fuseboard via the neutral, the stat, when the cylinder water reaches 60/65c (stat setting) will then open its own contacts and stop the power flow until the water temperature drops by ~ 8C to re close the contacts and restore the power flow.

eurokev · 18-07-2023 07:24PM

Yeah, the plumber bypassed the thermostat.

It's a two minute job to fix.

The brown wire needs to be moved to the "input" of the thermostat.

You could do it yourself but you'd have to make sure, 1) that the supply is isolated and 2) that the cables are making good connection and are screwed down well, so the copper of the cable is making good contact. If you are not sure, get someone who has confidence with that or try and get an electrician.

As others said earlier, that black tank you have is not for storing hot water, this stores the cold water for the cylinder but also serves as a dump vessel for your cylinders PRV, to stop the cylinder from blowing up

There's no point in dealing with the plumber, he is clearly an incompetent cowboy. Just take it as a lesson learned and hope that no lasting damage has been done to your installation

Hot water tank is boiling over. Scolding hot showers.

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