Hi all,

what are your thoughts regarding the following: I have a solar panel (evacuated tubes), the controller is installed indoors on the hot water cylinder cupboard wall ( visible all the time from the hallway, so I know instantly if there is water for a shower or not...).

as you know, the controller requires (at least) two temperature sensors, for the HWC and for the solar panel header. My issue is that I noticed some erratic behavior which occurs quite often. Everything is fine in the morning until the controller starts the pump. After that, the panel temp shows that it either keeps RAPIDLY going up (99C is the max temp on display) or drops after the pump starts (as expected), but the temp does not drop enough for the pump to stop. It is set to start the pump on dT of 15C and to stop it at dT of 4C (dT between the HWC and the water in the solar collector). Because the temp reading for the panel does not drop, the pump keeps going continuously. The temp rises to ((C in a matter of 15-20 sec, I am absolutely sure this is an error, the panle does not heat the water in the collector that fast.

I bet this is because the approx 12-13m run of cable from the controller to the outdoor temp sensor is done with ordinary wire like the telephone wiring, twisted red and white, silvery looking inside (solid, not mult-strand). It appears to me there is interference from the power wiring serving the circulation pump, wiring which runs fairly close to the temp sensor wiring - not really near it, but approx 200mm.

I am looking at replacing the temp sensor wiring with a screened cable (which should have been used from the beginning). How good results can I expect if I use a 15m USB cable (off TradeMe) or a 15m "2RCA-to-2RCA cable"? These are definitely screened, so it should do the trick... (cut the original connectors). The RCA cable is around $9 and the USB is approx $15 (for the 15m long cables).

Cat5, CAT6 - these are all screened, and fairly inexpensive ($8 for 15m on TradeMe)- I guess they would be a good candidate as well?

The higher the temp to the sensor, the higher the sensor's resistance (I believe it is a PT100 probe?), so if the temp goes up that is also consistent with a faulty contact (which would add more resistance to the circuit which would appear as higher temp recorded). I have checked the contacts and appear to be in good condition, they are not loose or corroded.

Many thanks in advance for your comments.