Pool heater cycles on and off incessently - how to fix?
I have a Stayrite Max-E-Therm 400 gas heater that was installed when I bought my house in March 2009. It's a fairly powerful heater and when working correctly, it'll quickly get the spa or pool to a nice temp.
In recent months it's been doing something odd. The heater will kick in as expected right after the switch is flipped but after about 45 seconds or so, the "Service System" light goes on and the burner shuts off (but not the blower). After about 45 seconds, the red service light goes off, the green "Heating" light flashes, and then the burner kicks in again (the heating light goes solid at that point). This cycle repeats endlessly, significantly extending out the time needed to get the spa or pool to the right temps.
According to the manual, a "Service System" light is a good indication of some sort of flow problem. While I do have a variable speed pump that is generally set at a low flow rate for purposes of economy, this problem occurs regardless of whether I'm running the pump at the lowest speed or in high speed vacuum mode.
The manual also talks about the heat exchanger possibly being blocked through the accumulation of "scale formation on the plaster or in the heat exchanger tubing". This sounds plausible. My salt generator gets significant build up on the electrodes in just a few months, so much so that I have to dunk it in an 4:1 water:acid mix bath every once in a while to get the hard white deposits out. The culprit is overly alkaline water but despite dumping a whole lot of muriatic acid into the pool on a regular basis, I'm only at about 7.8 ph (and getting it that low was a relatively recent development).
So what I've wondering is whether I should try go see if there is a way to clean out the pipes in the heat exchanger. It wouldn't surprise me at all if over a period of almost one fiscal year the high pH water would have deposited enough crud into the heater's internal pipes to interfere with the flow and triggering the above mentioned cycling.
Kicking up the pump to high doesn't help dislodge the accumulation. Unfortunately, I can't see any easy way for getting access to the heating coil. If indeed there is no access to the coil directly, I was wondering if I should try blocking the heater's outlet line (the salt generator is in-line past the heater exit and should be easy to remove it and plug the pipe), removing the PVC pipe to the inlet line, and then filling up the interior with a mix of 3:1 water\acid. After letting the acid mix do its stuff, I'd drain the heater with the hope that any junk would have dissolved.
Does this sound like a good idea? Got any others?