Interesting Thermosyphon effect

I finally swapped my standard Geyserwise Max display boards with the WiFi option and I must say it works great in HA using the TuyaLocal addon.

Looking at some of the data I noticed on extremely cold days the Anti Freeze kicks in and circulates hot water to prevent the collector freezing. One thing I did notice is my main geyser seemed to do this at a temperature above the Anti Freeze set point.

On closer inspection I found that it’s the thermosyphon effect kicking in and then continuing through the night and pulling my geyser temperature down until the next morning. I would never have seen this if I didn’t have the new WiFi display boards. Here is the graph showing the breakthrough of the cold water pushing hot water to the collector and then it just keeps going. From what I read a trap is one option but some guys says it only works partially. A more complete fix is a NRV in both cold and hot water feeds. I don’t know if I am keen to pay a plumber to come and install NRV’s but I thought this is a nice picture showing the effect seen below and how it affects the efficiency of your geyser.

1 Like

So you rely on thermosyphon (no water pump)?

No, I have a pump.

What I meant to say is that it’s interesting to see how natural thermosyphon eats away at my geyser hot water at night all by itself when the pressure of the cold water to drop from the collector and the hot water wanting to rise to the collector overcomes ‘gravity’ (not really gravity but once at a certain cold enough temperature it starts to flow faster).

If you don’t have a pump, an NRV will kill your efficiency during the day as well. What you need is an anti-syphon loop on the hot side.

1 Like

This isn’t thermosyphoning but rather convection. I presume the collector is mounted above the geyser so yes, the hot water will rise from the geyser.
Which line is the pump installed in?

How do you then stop the potential freezing?

Oh yeah, I forgot about that. In a pumpless system, you need to either live somewhere that it doesn’t get that cold, or have a indirect system with propylene glycol filling the loop. Those are the only sane solutions.

1 Like

All I am saying is that the NRV’s would decrease the geyser heat loss.

The point being, without having my geysers in HA I would never have seen this and this would keep on happening every night. I am keen to see what happens in summer when the low’s are higher than we have now.

Here is a crude illustration of what I am talking about.


I misread. I thought you have no pump. If you do have a pump, you need a spring-loaded NRV on the cold side after the pump, as well as an anti-syphon loop on the hot side. That is a U-loop that goes down for ~0.5m and up again, with a gap between the up and down and properly isolated.

The NRVs usually start leaking after a year or 2 due to scale build-up, which will cause syphoning even if the leak is miniscule/almost imperceptable during testing.