Hot tub jets and heater turning off to fast

SOURCE: Vibrations and banging when heater is turned on

wow! That heater that you have is meant for a very large swimming pool, quite a bit oversized, i bet i gets the job done quick though. I have seen before that somebody plumbed in a heater backwards, there are elevated arrows on the black manifold of the heater, make sure inlet and outlet are plumbed in correctly. Make sure you get your water tested. Because the water in your hot tub is no circulating as often (I assume) as a pool would be, the stagnate water sits inside the heat exchanger. What can happen, for instance, if you have high calcium, is the certain tubes inside the heat exchanged can get so clogged with calcium and they are completely shut and the banging noise is due to excessive heat build up inside the heat exchanger. This can ruin a heat exchanger very quickly and the heat exchanger is half the cost of the heater if you were to get a new one. You can check and see if tubes in the heat exchanger are clogged by taking the manifold off of the heat exchanger, and shining a flashlight down the different tubes. However you have to disassemble quite a bit to actually be able to do that.