Identifying limescale in a hot water cylinder?

[steve-o]

Hi there,

I have a 20 year old hot water cylinder, which is heated from an oil boiler (aga), and has an electric immersion element as well.

I don't get much hot water out of the system before it turns cold, and I've been told it might be limescaled up and need replacing.

I installed 4 temperature sensors to monitor what happens:

1. Attached to the hot water outlet at the top of the tank (with insulation and cable tie)
2. Attached to the oil boiler inlet and outlet at the bottom of the tank (with insulation and cable tie)
3. Attached to the tank 1/3 of the way up (with insulation) - I read this is the standard placement of a thermostat

I also manually measure hot water temperature out of a nearby tap, and it is around 10C higher than the "hot_water" measurement - i.e. I am getting 60C out of the system so happy from a legionella point of view.

My observation is that the temperature 1/3 up the tank never gets above 40C. Is that an indicator that there is a load of limescale at the bottom of the tank?

Is it normal that, when run, the hot water temperature drops significantly (20C) in about 5 minutes?

Cheers,

Steve

 

[exedon2]

In simple terms if your in a hard water area after 20 years of been heated by a a oil aga the coil in the cylinder will be well scalded up.
If cylinder is changed seriously consider installing a water softener worth every penny.

 

[SJB060685]

My observation is that the temperature 1/3 up the tank never gets above 40C. Is that an indicator that there is a load of limescale at the bottom of the tank?

I suspect as you say the bottom third of the cylinder is laden with limescale. The only real way of telling is draining the cylinder and having a look, although if you're in a hard water area and have a 20 year old cylinder im willing to bet there is a fair amount.
When heat is passed through the cylinder coil, in this case by gravity circulation you will generate convection currents within the stored water. This will heat up the water until thermal equilibrium is reached, there might be a few degrees difference between the top and bottom of cylinder but shouldn't be what you've observed.
As exedon has mentioned above you should consider tackling the hard water issue, which can be done by a number of ways, otherwise, overtime it will just build up again.

 

[steve-o]

Cheers I'll bite the bullet and get a new tank in. I'll reinstall the sensors and will share what the values are.

 

[Reddwarf4ever]

Hi there,

I have a 20 year old hot water cylinder, which is heated from an oil boiler (aga), and has an electric immersion element as well.

I don't get much hot water out of the system before it turns cold, and I've been told it might be limescaled up and need replacing.

I installed 4 temperature sensors to monitor what happens:

1. Attached to the hot water outlet at the top of the tank (with insulation and cable tie)
2. Attached to the oil boiler inlet and outlet at the bottom of the tank (with insulation and cable tie)
3. Attached to the tank 1/3 of the way up (with insulation) - I read this is the standard placement of a thermostat

View attachment 45942

I also manually measure hot water temperature out of a nearby tap, and it is around 10C higher than the "hot_water" measurement - i.e. I am getting 60C out of the system so happy from a legionella point of view.

My observation is that the temperature 1/3 up the tank never gets above 40C. Is that an indicator that there is a load of limescale at the bottom of the tank?

Is it normal that, when run, the hot water temperature drops significantly (20C) in about 5 minutes?

Cheers,

Steve

Hello could you share what method you used to monitor the temperatures ? Am looking for a system of sensors for my boiler and immersion cylinder to send the data to an Mobil phone app. Best I can find is a 6 probe cook device, but the probes have to all be in close proximity to the device as they plug into it. Thanks

 

[steve-o]

Hello could you share what method you used to monitor the temperatures ? Am looking for a system of sensors for my boiler and immersion cylinder to send the data to an Mobil phone app. Best I can find is a 6 probe cook device, but the probes have to all be in close proximity to the device as they plug into it. Thanks

Sure thing. I'm using the Home Assistant platform to bring in data from various places.

For the immersion cylinder, I made a sensor board with a NodeMCU and ds18b20 temperature sensors. There are off-the-shelf options with Home Assistant, like a Shelly with Temperature sensor add-on.

 

[Reddwarf4ever]

Sure thing. I'm using the Home Assistant platform to bring in data from various places.

For the immersion cylinder, I made a sensor board with a NodeMCU and ds18b20 temperature sensors. There are off-the-shelf options with Home Assistant, like a Shelly with Temperature sensor add-on.

Thanks