I hadn't used the Hayward H150 heater for 2 years. The pool has been open and running for about a week and all had been heating normally. I had someone spray a finish on the surrounding deck. The over spray got in the pool and clogged the DE filter which I dealt with. Seemingly about the same time the heater began heating only marginally. I'm not sure if the finish going through it is the problem or not.
The burners are clean and fully firing. I took the manifold off the heat exchanger and snaked the copper tubes to be sure there were no obstructions. The exchanger is clean and clear and in fine shape. The one fault I found was the bypass which looks like a car thermostat was inoperative, frozen in the shut position. I couldn't get one immediately so I put it back together without the bypass. It still does the same marginal heating. I'm going to get the new bypass but it doesn't seem to be the problem as it operates the same with the bypass closed or with the bypass not there.
I do have a diverter valve and I reduced the flow through the heater until it make knocking noises from steam and then added back enough flow to stop that and still same results.
So I'm stumped. What could cause a fully firing heater that has a clean as a whistle heat exchanger to only marginally heat? Days before the heater heated just fine with noticeably warm water coming through the return jet. It now produces water that is barely warmer then the pool water through the jet.
Any help would be much appreciated.