Hot water cylinder does not seem as hot

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SomeoneSomewhere

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#3327911 5-Jan-2025 21:10

I have seen a failed thermostat result in about ~45C temps. The plastic housing around the adjustment screw had failed, so it no longer had adequate spring pressure.

If you operate the TPR valve (safety valve at the top of the cylinder), this will dump hot water into the safety drain, before the tempering valve. Measure the temperature of that water using e.g. a meat or body thermometer.

IR thermometers are not usually very good at measuring water temperature.

jlittle

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#3327970 5-Jan-2025 22:26

MadEngineer:
The thermostat should be set to 60degrees C....

I thought it was dangerous to have the cylinder less than 70 C, for fear of Legionnaire's disease. And also dangerous to have the hot tap over 60 C, for fear of scalds. So that's why there are tempering valves.

Jase2985

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#3327980 5-Jan-2025 22:55

jlittle:
MadEngineer:

The thermostat should be set to 60degrees C....

I thought it was dangerous to have the cylinder less than 70 C, for fear of Legionnaire's disease. And also dangerous to have the hot tap over 60 C, for fear of scalds. So that's why there are tempering valves.

Hot water cylinders must be set at a temperature of not less than 60°C for Legionnaire's disease, and the maximum hot water temperature at the tap should be 50°C for residential buildings through the use of a tempering valve

SomeoneSomewhere

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#3327981 5-Jan-2025 22:56

Temperature allowed at the tap has been reduced to 55C and now to 50C: https://www.building.govt.nz/building-code-compliance/g-services-and-facilities/g12-water-supplies/preventing-scalding-from-tap-water

I'm not certain on the current legal requirements for legionella control, but its a time-or-temperature thing. 70C for a few minutes every few days is adequate, but if you're in the 60C range or a bit below it needs to be maintained for a few hours more-or-less daily.

Goosey

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#3328104 6-Jan-2025 08:46

Sorry, when I said thermostat before, I meant element !

if you are in an area with water chlorination, unfortunately you will have to replace elements especially if the local council has been going hard e.g. you can smell it often.

in chch, many elements failed a few years back, it was becoming an epidemic however in the past couple of years (as the council has replaced well heads and reduced chlorine dosages, the epidemic has eased and nowadays it’s just back to usual replacement cycles).

Spyware

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#3328120 6-Jan-2025 09:41

Goosey:

Sorry, when I said thermostat before, I meant element !

if you are in an area with water chlorination, unfortunately you will have to replace elements especially if the local council has been going hard e.g. you can smell it often.

I thought the cylinders themselves were failing and leaking contents.

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SomeoneSomewhere

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#3328318 6-Jan-2025 14:38

That too.

Steel ('vitreous enamel') cylinders generally have a sacrificial anode that should be replaced every 1-5 years; this is rarely if ever done in NZ so it runs out of material and the cylinder starts corroding.

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Goosey

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#3328342 6-Jan-2025 17:03

Spyware:
Goosey:

Sorry, when I said thermostat before, I meant element !

if you are in an area with water chlorination, unfortunately you will have to replace elements especially if the local council has been going hard e.g. you can smell it often.

I thought the cylinders themselves were failing and leaking contents.

That too… but elements were popping first. Actually popping open (I have photos somewhere).
Mainly the older cylinders leaked.

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