ESD != Earth bonding.
Yes, sorry I meant the fact I have low voltage probes connected to copper pipes. In the UK (and most places?) the copper pipes form part of the Earth circuit of the house. I'm sure some grey beards will tell me this isn't worth considering, but I seen the potential that an Earth fault in the house, could see the copper piping could surge to 240V if my circuit presents a better route to Earth than the rest of the pipe it could take current.
On the ESD. If the NodeMCU has inheritied charge from the carpet and the USB charger is floating, it is still fine is it has 10000V and 10005V input... unless I move it

But yes, I need cases, that's the purpose of the project.

I wonder a bit that the in and out-flow temps are so close together. It seems you don't take much heat from it even as the system heats up the water. But I'm no expert here.
It's interesting and only because I fitted those probes do we know this is the case. They are definitely reading right. It's a sign my heating system is old and tired. The pump rate is probably to high and the radiators too old and gunked up that it's not taking as much heat as it could from the system.
If you do some sums, OUT temp - IN temp is about 2*C. An estimate of the total water volume in the system and an assumption is circulates uniformly results in a sizable amount of kW. I don't have the numbers on hand, but I did them. It was well below the boiler output though, maybe 25% of it. If I was keeping this system I'd swap out the pump for a slower flow rate.
EDIT: It also has to be considered I have an inline heat exchanger in the hot water tank, so that will act as a ballast or temperature buffer in the system.
I am having my whole heating changed from oil to gas next month, with a few radiators being replaced and the system flushed and will draw a new baseline there.