Adding extra temperature sensor to hot water tank

[Harry Bloomfield]

The NTC negates the use of the cylinder stat, that is unless you are using the backup immersion heater which utilises the stat for the immersion and boiler control if required.

Mine, connected I think to a VR65, I fitted into the thermostat pocket of the immersion heater, after removing the thermostat first. The immersion heater is only for backup, and it's circuit has been diverted for other purposes, but could be easily recommissioned if needed.

 

[Pete the Feet]

Same here Harry. What I should do is do what I tried out and place the NTC alongside the thermostat boss as I have done with the additional sensor next to the outlet boss. I just placed the thermostat on the floor at the back of the cylinder. Not good practice, even if it is out of the way. I think I was probably erring on the side of caution as the NTC actually controls the boiler whereas the extra sensor is just there for information.
I won a pump on ebay recently and received it last Friday. Therefore when I have time I will shut off and drain down the cylinder which seems to take an age, then fit the pump. I will inform of my findings if anyone is interested. Sadly I do find it interesting; that's retirement for you.

 

[Harry Bloomfield]

I will inform of my findings if anyone is interested. Sadly I do find it interesting; that's retirement for you.

Yep, always interested! I was wondering if it might be worthwhile to add an extra NTC, with a two-way switch, to select the default NTC, or a second one at a higher level - 1/3, 2/3 up from the bottom. I just wasn't sure how well stratification worked with the heating coil at the bottom.

My VRC 470f can display the NTC's temperature, on the display.

 

[Pete the Feet]

I think the pump will even some of the temperature difference. I was going to use a spare Tapo smart plug and schedule the pump. Another option I thought of was a dual system of using the feed from the DHW demand, i.e. zone valve and the Smart timer plug. I would have to use two relays for this. However at some pont in the future the Mrs may have to inherit the House that Jack built and whilst I'm here there is no problem but if it goes belly up after my demise then it may be beyond the comprehension of the muggins who will have to ultimately fault find and rectify my indulgences. The Mrs is getting the hang of the basic workings of the VSMART app I installed on her phone so there is promise.
I like the ability of the VRC470f that you have, which displays the DHW temperature and utilises the outside air temperature to modify boiler flow temperature. This is an often overlooked energy saving feature in a domestic system. Utilising the outside air temperature is usually confined to commercial systems.

 

[Sammy21]

here is my setup using an old Sonoff TH10:

I've not found a way to log the temperature yet, but once I've got that sorted I'll spend a couple of weeks logging the temp before changing my heating strategy.

My thinking is that I'll cut out the morning heating cycle which runs for an hour currently, and change this so that the sonoff switches on the boiler and heats the tank but only if the measured temp drops below, say 40C, in which case it'll heat the water until it gets to 45C and then stop.

It would be great if there was a way to log all the boiler burns on a chart too, but I doubt there is an easy way to do this. The switched live on the Sonoff goes straight to the DHW terminal in the wiring box, so it can switch on the water independently from the Wiser controls, giving me both scheduled and temperature based controls. In fact, I don't need the wiser DHW controls at all any more, in theory.

Drilling the hole for the sensor was scarier than I thought, as the boiler sleeve is sheet steel, and once you pimch through, the insulation provides no resistance whatsoever! So be careful. Still not sure if I have the best contact between the sensor and the tank surface, so am experimenting with tin foil to see if I can increase the quality of the contact.

 

[Pete the Feet]

I too have a Sonoff TH10. On my cylinder there is absolutely no need to drill the insulation as you have done. In fact drilling the insulation as you have done will only give the sensor point contact on the end of the sensor. I just poked my sensor in at the cylinder outlet boss thereby getting more contact on the cylinder wall. Just take a closer look at your cylinder to see if this is possible on any of the pipe connections, flow or secondary return. There will be a connection point for secondary return, even if it is not used.

 

[Harry Bloomfield]

It would be great if there was a way to log all the boiler burns on a chart too, but I doubt there is an easy way to do this.

NTC, connected to a RasberryPi, with the NTC attached to the boiler flow pipe. Set the Pi to log when the flow temperature rises above a set temperature.

 

[Sammy21]

NTC, connected to a RasberryPi, with the NTC attached to the boiler flow pipe. Set the Pi to log when the flow temperature rises above a set temperature.

smart. I have another TH10 I could use for this. Good for marking the start of a burn, harder to isolate the end maybe? Coud attach sensor to the DHT tank inlet pipe maybe, but it will likely retain heat for quite a while...

 

[Sammy21]

I just poked my sensor in at the cylinder outlet boss thereby getting more contact on the cylinder wall. Just take a closer look at your cylinder to see if this is possible on any of the pipe connections, flow or secondary return. There will be a connection point for secondary return, even if it is not used.

Unfortunately, there are no cunning gaps I can use, worse luck! And no unused ports...

 

[SpecialK]

If you want graphs use home assistant..

 

[SpecialK]

here is my setup using an old Sonoff TH10:


I've not found a way to log the temperature yet, but once I've got that sorted I'll spend a couple of weeks logging the temp before changing my heating strategy.

My thinking is that I'll cut out the morning heating cycle which runs for an hour currently, and change this so that the sonoff switches on the boiler and heats the tank but only if the measured temp drops below, say 40C, in which case it'll heat the water until it gets to 45C and then stop.

It would be great if there was a way to log all the boiler burns on a chart too, but I doubt there is an easy way to do this. The switched live on the Sonoff goes straight to the DHW terminal in the wiring box, so it can switch on the water independently from the Wiser controls, giving me both scheduled and temperature based controls. In fact, I don't need the wiser DHW controls at all any more, in theory.

Drilling the hole for the sensor was scarier than I thought, as the boiler sleeve is sheet steel, and once you pimch through, the insulation provides no resistance whatsoever! So be careful. Still not sure if I have the best contact between the sensor and the tank surface, so am experimenting with tin foil to see if I can increase the quality of the contact.

You could use some thermal paste on the end of the probe?

 

[Sammy21]

If you want graphs use home assistant..

View attachment 294399

pretty! home assistant could be a little beyond my capabilities right now...

 

[Sammy21]

You could use some thermal paste on the end of the probe?

i thought about that but thought it might get a bit messy in there? what about adding a small cylinder of tin foil to the end that i can compress against the surface of the boiler?

 

[Pete the Feet]

Yep, always interested! I was wondering if it might be worthwhile to add an extra NTC, with a two-way switch, to select the default NTC, or a second one at a higher level - 1/3, 2/3 up from the bottom. I just wasn't sure how well stratification worked with the heating coil at the bottom.

My VRC 470f can display the NTC's temperature, on the display.

Just an update Harry. I installed the pump a couple of days ago. The pump is installed between the outlet and cold water inlet. I installed a double check valve prior to the pump and one on the cold water feed prior to where the pump tees into the cold water feed if you get my drift [If not I will try to explain better]. The pipe immediately after the the pump gets mad hot when the pump is activated but cools off after a foot. The system pressure is about 3.5bar and I'm not sure as to the "actual" flowrate of the destratification pump under these conditions. I expected a more rapid flow of water but it does work when I check the boiler readout where the sensor is at a similar level to the cold water inlet and the outlet Sonoff sensor. What I have noticed is that the 1 hour I have set the DHW to heat up the 300L cylinder is not enough to heat it up to anywhere near 60C from a 40C baseline. I will make adjustments as required as I do not want legionella in the system.

 

[Pete the Feet]

If you want graphs use home assistant..

View attachment 294399

This is sadly very interesting. How do you do this from a Sonoff TH10?