Hot water cylinder temp

Buckster · 3 Oct 2020 at 11:00

Moved into a new house about a year ago

House has fairly standard heating/water with an indirect (Joule) hot water tank

Thermostat on front though is set to somewhere about 48c which seems quite low - was provided the commissioning paperwork and a temp in the 40s was hand written on there (can't remember exact value) so temp obviously deliberate

Will try and query with builders but any idea why would be set so low please ?

Because house was expected to not be lived in for a number of months and they set a bare minimum temp ?

Experience that the thermostat maybe under reads temp ?

Looked at manual and seems.to suggest a higher water temp

Water from taps and showers seem hot

Any ideas please ?

pp111 · 3 Oct 2020 at 14:49

Thermostat on the front of what? Are you talking about the one on the front of the boiler or the hot water tank? I am assuming you mean the one on the front of the tank. The temperature setting on the boiler ( usually not in degrees ) sets how hot the water is before the boiler switches off ( This is usually set somewhere around 70~80 degrees ). This represents the maximum temperature of the water tank and radiators. But when the boiler heats the tank the hot water floats on top so the top temperature will very quickly reach the boiler temperature ( 70~80 ). Over time the temperature of the entire tank will rise as the boiler pumps more and more heat in to it. The more heat in the tank the more the lower parts of the tank will be warmed. The thermostat is not at the top, it's 2/3 the way down, so you can think of it as measuring the amount of hot water in the tank. 48 Degrees is not unusual.

RJC · 3 Oct 2020 at 15:03

I assume this is not the immersion heater thermostat?

Only way to tell is to turn the hot water on and adjust the temperature higher or lower if possible.

Buckster · 3 Oct 2020 at 15:21

Thanks for replies this is the thermostat on the hot water tank itself and is separate to the immersion heater

It is indeed about 2/3 down maybe it is like you said just as it allows for the temperature delta top to bottom

I've looked at commissioning documentation

It says

'What is the hot water thermostat set temperature ?" Hand written in box is 44c

I'll post up some pics

Only asked as seemed low

Danm54 · 3 Oct 2020 at 19:03

It is low, you want it reaching 60 degrees or so at least once a week I believe.
Have a google on legionella and what temps you need to achieve to kill it.

Mysterae_ · 4 Oct 2020 at 09:39

As @Danm54 says, you'll want a higher temperature cycle at least once a week to kill off any legionella.

On my old water tank the temp sensor was set at 55c, not sure if that was for the immersion heater element or for the heating satisfied signal to the boiler.

bainbridge · 4 Oct 2020 at 10:49

The main thing here, explained by previous posts, is the temp of the water coming out of the tap. In our house I set the temp to 55c and was getting 70-75c out of the tap. After some trial and error by setting the temp to 40c we get 55c out of the tap.

fezster · 4 Oct 2020 at 11:41

A vertical cylinder will suffer from stratification, which means the water at the top will be far hotter than that in the middle or the bottom. To ensure legionella does not develop (however small the likelihood), the majority of the tank should be heated to 55-60 degrees, at least once a week, not just the very top.

OP - unless you have some controls which ensure the tank is heated to 60 once a week (which is unlikely if there is a mechanical stat on the front cutting it out at 48), you should increase the temperature. If you had a G3 service done, they should measure the temperature of the water, and increase it accordingly.