Hot water getting too hot.

tibby1947, Jan 27, 6:25pm
Recently noticed hot water from cylinder is a lot hotter than before. Cylinder has date of 2001 on it. No adjustment dial, all hidden by metal plate. Please advise best thing to do? Partner is diy ok but safety first too. At moment we have turned power to cylinder off.
johotech, Jan 27, 6:50pm
Call an electrician to replace the thermostat probably.
delshamic, Jan 27, 7:44pm
the cold water is now not very cold which affects shower temp
tegretol, Jan 27, 8:57pm
Turn the bloody thermostat down. Anti-clockwise.
maclad, Jan 27, 9:01pm
So how will that help if this is a new thing, if thermostat is faulty this won't help
tibby1947, Jan 28, 4:13am
Thanks for replies.
johotech as it’s a long weekend am I correct in turning power to cylinder off until I can sort electrician out?
delshamic, water red hot out of taps too, not only shower.
tegretol, as said, no adjustment knob visible ie thermostat control.
maclad, yes only been too hot for past couple of days which indicates something just happened.
lythande1, Jan 28, 8:35am
The cold water is not anywhere near as cold.
It is not a faulty thermostat.
Ours is like this too, always is in summer.
trade4us2, Jan 28, 9:09am
It is probably a faulty thermostat. You could turn the power to the cylinder on for a couple of hours every day until the electrician arrives.
There's no good reason why the thermostat would go out of adjustment or weld its contacts together, but that seems to happen. Mine is now 25 years old.
pauldw, Jan 28, 9:37am
Made in a factory that probably lost the contract to some place cheaper.
tweake, Jan 28, 10:35am
metal does change with use. the bimetallic strip bends a bit different as it gets older.
i doubt its welded the contacts has it will boil the tank and eventually burn out the thermostat and stop working.

the other thing that can happen is if you have controlled hot water and its actually the controlled supply thats inadvertently controlling the temp.
i get that on mine because i don't use much and often its not cold enough for the thermostat to be on at the same time as the power is on. so it misses one of the power on times. but now and then it hits both times and you end up with very hot water compared to what you normally get.
tibby1947, Jan 28, 8:51pm
I am happy to do this ^^^ thanks.
nzjay, Jan 29, 11:30am
I've struck some weird ones over the years as a sparky. A very small leak from a pressure reducing valve or over pressure valve CAN cause a small continual input of cold water into the bottom of the tank, cooling the thermostat, causing the element to switch on. Because of the small leak, the element is on much longer than it would normally be. Hot water off the continually running element, rises and accumulates at the top of the cylinder at a higher temp than it normally would be, ready to be drawn off.
It has to get really hot at the top for the heat to build down to thermostat level and turn it off.

Another one is an element that has a hole in it from lime corrosion that is near the live end of the element (ie not the neutral end). Not drawing enough power to blow a fuse, but allowing the cylinder to act like an electrode boiler. The flow of current through all the water to earth somehow causes the temp to rise at the top of the cylinder. So a faulty element can cause this phenomena as well. Obviously this is easily tested using a meter. tracking down small leaks can be harder.

Nothing wrong with the thermostat in both these instances.
mrcat1, Jan 29, 12:55pm
It could be from a leaking ajax valve seal allowing water to bypass onto the roof thru the overflow.
Have you checked to see if the overflow is not running over as this will also increase power and heating issues.
tibby1947, Jan 29, 5:10pm
Overflow checked and not running, thanks for hint.
ianab, Jan 30, 8:06pm
I've had to replace the thermostat in my hot water 2X in the 15 years I've lived here. First one was probably the original (~50 years old) and the contacts had just worn away. (There is a small arc each time it turns on or off) It either didn't make contact (cold water), or welded itself shut and boiled the cylinder. No problem, got local sparky to swap it out, all good. Then a couple of years later, same thing. Another new thermostat, this one designed for a larger dairy shed heater. Had a close look at the old one, and the contacts were visibly burnt up (and yes the volts / amps rating was correct on it) It was just a crappy thermostat.

Either way, 99% chance you just need a new thermostat. The old will have burnt contacts that are sticking "ON" and overheating the water.
aredwood, Jan 30, 10:53pm
Other options, Tempering valve jammed on full hot, Instead of mixing the hot and cold. Or the OP has solar hot water, more sun means hotter hot water.
tibby1947, Feb 1, 1:28pm
OP here. no solar hot water.
Found receipts, boiler replaced in 2001.
Thermostat replaced in 2010.
Took panel off, temp was set just below 60. Moved back a fraction to 57.
Power been off a couple of days but on now so will see if it works or not.
Sparkie then and maybe another $250 bill, in fact that was 2010 and at $60 an hour so will be more now.
trade4us2, Jan 3, 2:46pm
In my experience, the temperature gauge on thermostats is not very accurate, and the gauge may change over time.
My hot water cylinder is next to the kitchen sink, of course. Where else would it be put and why? So I run hot water into a cup and measure the temperature with a thermometer that can read up to 60 degrees. It's probably worth buying one of those. A meat thermometer might do.
At that temperature the water is too hot to hold a finger in for more than a couple of seconds.
Once the water is the right temperature, turn off the power and adjust the thermostat until you can hear it clicking on and off. If it doesn't click off then the thermostat would need replacing.

My system was installed before tempering valves were required, so I don't have one. If you have a tempering valve you will have to pay an expert to sort it all out. If young children or elderly people might burn themselves you might want a tempering valve, although expert opinion these days is that they are always installed wrongly, and plumbers don't understand or don't care.