Fixing a solar hot water controller
10:28am 1st October 2012
Fixing a broken solar hot water controller need not be that expensive
We have had a Hills Solar evacuated tube solar hot water heater for a number of years now that provided cheap hot water year round. Recently we noticed that our hot water was not as hot as we were used to it. We put it down to a cold and cloudy winter. Although once we noticed that even on sunny days there was not much hot water available it was clear something was wrong.
So under the house I go, we have a system where the hot water tank
is fitted in the crawl space under the house at the end where you can easily stand. Now a quick touch test of the return pipe where it goes into the hot water tank showed there was not much heat.. Hmm, a quick look at the solar controller showed that it thought it was powering the pump, the light was on. The pump must have gone I thought, but these small pumps are very reliable. I wondered if the controller itself was to blame, so I turned it off and turned it on, then when the light came back on I could hear the relay 'click' and the pump started up. So the relay had stuck.
So thinking I might have fixed it, I left it a day and came back and had another look at it. Same thing, the light was on but no pumping going on. So this time I flicked my finger against the controller box and that was sufficient to make the relay set and conduct.
So the relay was 'shot' (very technical term). Now I got hold of the company through which I bought the system, they quoted me $125 for a replacement second hand controller or $250 for a new one. They also suggested (to their credit) that I could just replace the relay and see if that would sort it.
Wanting to avoid such expense I dismantled the controller and found the relay was a standard 12v coil with SPDT (Single Pole Double Throw) mains rated. In fact it was a rather low end relay operating at its make and break ratings (usually one has a relay with its make and break ratings well above the load, so it will last a long time). So I just unsoldered it and replaced it with a much higher rated relay from my 'stock' of electrical bits. Put the board back in and applied power and was rewarded with a nice strong 'click' and the pump was on and pumping.
Since this fix we have enjoyed again low cost hot water.
Whats the learn from this - if you find you are without hot water and the controller thinks it has the pump on, give the controller box a good flick - if it comes on, you have a bad relay which can be replaced for as little as $10..