immersion won't heat above 50c

touchdown77

My 3kw immersion won't heat water above 50c, I've replaced the stat, thinking that it was misreading but even with a new stat (turned up to max) the water won't heat above 50c.

Its a 3kw, heating about 250l, on night rate electricity.

I've an owl monitor connected and it shows that the immersion runs from 11pm for about 2hrs, then cycles on and off till it turns off at 8am.

The cylinder etc is only 3 months old, so limescale isn't an issue, plus I've a water softer connected before the immersion.

Any suggestions whats going on?

CJ Haughey

Is it at the taps you are measuring the 50 degree? If it is quiet possible you have a mixing valve on hw.

touchdown77

CJ Haughey wrote: »

Is it at the taps you are measuring the 50 degree? If it is quiet possible you have a mixing valve on hw.

Temperature is being measured at top of cylinder so no, its not mixed.

solargain

Any chance its on night rate and you have a hortzman 7 controller on it ??, or on night rate and controlled through a devi-reg controller in the board along with night storage heating. I have come across some funny things done in apartments lately

touchdown77

solargain wrote: »

Any chance its on night rate and you have a hortzman 7 controller on it ??, or on night rate and controlled through a devi-reg controller in the board along with night storage heating. I have come across some funny things done in apartments lately

its on a standard apt rotary time switch which I've set to be on from 11 to 8am. I could put it on during the day but no need for it.

If I check it at 7am, its still live so it doesnt appear to be a power interruption issue.

Bruthal

What are you measuring the temp with, and exactly where on the cylinder?

Cerco

At 250l that is quite a big cylinder. I think the standard ones would be about half that size.

touchdown77

Bruthal wrote: »

What are you measuring the temp with, and exactly where on the cylinder?

Using a temp probe at the hot water outlet at the top of the cylinder. I also measured the temperature at the nearest tap and they are about the same.

At 250l that is quite a big cylinder. I think the standard ones would be about half that size

Yes but if the element was struggling to heat the cylinder, wouldn't it be running all night and never cutting out?
whereas in this case its reaching its own temp after about 60 to 90 mins.

Cerco

touchdown77 wrote: »

Yes but if the element was struggling to heat the cylinder, wouldn't it be running all night and never cutting out?
whereas in this case its reaching its own temp after about 60 to 90 mins.

Yes, and the fact it cycles after reaching the temperature suggests it is being controlled by the thermostat.
Is there anything else connected to the tank e.g an external cylinder stat?

touchdown77

Thanks to everyone for their replies so far!

Cerco wrote: »

Yes, and the fact it cycles after reaching the temperature suggests it is being controlled by the thermostat.
Is there anything else connected to the tank e.g an external cylinder stat?

No the wiring is dead simple, Immerstat time clock, wired straight to immersion, here's a pic of the immersion, the red stat turned up to the max.

Cerco

I cannot see what is connected to the second terminal on the stat.
I assume that brown lead is going to the element phase connection directly?

Dardania

touchdown77 wrote: »

Using a temp probe at the hot water outlet at the top of the cylinder. I also measured the temperature at the nearest tap and they are about the same.




Yes but if the element was struggling to heat the cylinder, wouldn't it be running all night and never cutting out?
whereas in this case its reaching its own temp after about 60 to 90 mins.

Is the probe immersed in the water, or touching the copper? What type of probe?

I'm wondering is there some sort of temp sensor inside the immersion element (wouldn't have thought so)

What is the contact with the normal stat to the cylinder like? Not wrapped in insulation, artificially inflating the temp?

touchdown77

Cerco wrote: »

I cannot see what is connected to the second terminal on the stat.
I assume that brown lead is going to the element phase connection directly?

The cables are wired directly from time switch into N and L terminals that you can see in the pic, no bridge cable or anything else.

Is the probe immersed in the water, or touching the copper? What type of probe?

No its on the pipe. However its measurement is confirmed by water temp from the nearest tap... I'm not aiming for 100% accuracy but need to be somewhere near 65c.

I'm wondering is there some sort of temp sensor inside the immersion element (wouldn't have thought so)

See pics below of the original stat that I replaced (thinking it was faulty but the replacement behaves in exactly the same way)

Escapees

Silly question but are you sure 50degC isn't the max limit for the stat? Often HW cylinders are set to 60degC max for safety reasons (to stop people burning themselves when using hot water) and 50 isn't too far away from 60degC...

CJ Haughey

Is the immersion the sole heat source of heating the cylinder?

touchdown77

Escapees wrote: »

Silly question but are you sure 50degC isn't the max limit for the stat? Often HW cylinders are set to 60degC max for safety reasons (to stop people burning themselves when using hot water) and 50 isn't too far away from 60degC...

I just checked the spec of the stat;

THERMOWATT RTS-3 181316 (RED DIAL)

Weight 0.1 kg
Preset Temp 65°C Max Op Trip, 75°C Safety
Length Inches 280mm
Thermostat Type Single Phase Rod / Stem Thermostat

So the stat should be allowing the element to reach 65c but it isnt.

Is the immersion the sole heat source of heating the cylinder?

Yes

Dardania

WHats the insulation on pipework from the cylinder to the tap?

Is it possible that you're reading the temp at tap by immersing in the stream (so accurately getting 50C) but by reading the surface temp of the cylinder at 50C, that the temp inside is actually higher (and the delta T from cylinder to tap is wasted to atmosphere?)

It feels to me the cylinder is reaching a temp then being controlled by the stat...you can see that by the hysteresis / on-off control on the owl

Bruthal

Test the temperature probe on a boiling kettle, see what it says.

touchdown77

Bruthal wrote: »

Test the temperature probe on a boiling kettle, see what it says.

OK great idea, So I just tested the temp at the closest tap using a digital cooking theromometer and its reading 50c which is 1c different to the probe at the top of the tank. So the readings are pretty accurate.

So the issue remains.

Any other thoughts or hunches...throw them at me.

I'm really stumped here, for the life of me, I cant figure out why two stats are cutting out at 50c instead of getting close to 65c

Cerco

Op, did this installation ever function normally or has it been like this from day 1?
Is this a dual element ? If so what happens when you switch between sink and bath? Does it heat above 50 on either?
Can you hear the thermostat clicking in and out as it appears to cycle?

Is there a pump connected to a coil in the cylinder?

Turn down the thermostat to about midway and see does it cut out at a lower temperature. This will indicate if the thermostat is functioning.
Test the temperature gauge as described by Bruthal above and if possible on another cylinder.

If you are sure your temperature gauge is accurate and thermostat is functioning then I would say the next step is to check the element itself.

You could , if you were comfortable/competent enough, to bypass the thermostat temporarily to check the element is capable of heating the load above 50 degC.
You would need to monitor this closely to ensure water does not boil and ensure nobody turns a tap on and gets a scald. Only try this if you are confident you know what you are doing.
As an aside you should be aware that at 50degC your cylinder could cause health issues due to bacteria. This reportedly can cause Legionella by persons breathing in during showering.

touchdown77

Op, did this installation ever function normally or has it been like this from day 1?

Its been like this from day 1.

Is this a dual element ?

Single element.

Can you hear the thermostat clicking in and out as it appears to cycle?

Yes, I'm pretty sure I heard it once.

Turn down the thermostat to about midway and see does it cut out at a lower temperature. This will indicate if the thermostat is functioning.

Did this ages ago and it seemed to heat water to lower temperature all right.

bypass the thermostat temporarily

I can't do that with this particular wiring setup as there is no link wire, the L goes into the unit direct from the time-switch so its not possible to bypass the stat.



I forgot to mention at the outset that this element is mounted horizontally. Would this have any significance?

Bruthal

Certainly looks like a stat issue, or temperature measuring error.

Cerco

Have you checked the timer?
If the timer was faulty, the apparent thermostat cycling, could be switching by the timer. Unlikely but still worth checking.

Bruthal

The funny thing is, a side fitted element with stat in same position, will heat top end of cylinder to a higher temperature than it's own set point.

But perhaps the stat is very close to the element, or directly above part of element, and is reaching set point due to local heating of water right beside stat pocket as the heated water rises , causing stat to switch after overall water temperature increases somewhat, but before it's a set temperature.

Remove stat and mix some water to 50 degrees and see if it clicks stat. Or put stat in pot and heat up. Monitor temperature, and point stat clicks at.

Cerco

Could there be a temperature limiting valve fitted to the cylinder outlet?
This would allow stored water to heat to 60 degC while limiting output water to 50 degC. by automatically mixing in some cold water.

Would look something like a tee connection on the outlet.

CJ Haughey

Cerco wrote: »

Could there be a temperature limiting valve fitted to the cylinder outlet?
This would allow stored water to heat to 60 degC while limiting output water to 50 degC. by automatically mixing in some cold water.

Would look something like a tee connection on the outlet.

I already asked op that and nothing present.

Cerco

CJ Haughey wrote: »

Is the immersion the sole heat source of heating the cylinder?

Apologies, I missed that.

Dtp1979

So is there another heat source?

meercat

Bruthal wrote: »

The funny thing is, a side fitted element with stat in same position, will heat top end of cylinder to a higher temperature than it's own set point.

But perhaps the stat is very close to the element, or directly above part of element, and is reaching set point due to local heating of water right beside stat pocket as the heated water rises , causing stat to switch after overall water temperature increases somewhat, but before it's a set temperature.

Remove stat and mix some water to 50 degrees and see if it clicks stat. Or put stat in pot and heat up. Monitor temperature, and point stat clicks at.

This is the most likely IMHO
The tube that the stat fits into may be slightly bent and touching the element preventing full heating of cylinder. That or there's a leak in your hot water system. Turn off inlet valve to cylinder and heat water overnight. Turn valve on the following morning and test temperature.

Bruthal

Cerco wrote: »

Apologies, I missed that.

Its actually post 2 he mentions possible mixing valve.

Second heating source is a different issue.

CJ Haughey

Dtp1979 wrote: »

So is there another heat source?

Already asked too.