I have a hot tub control that switches the heater element on and off to set the water temperature. The thermostat has 20 amp contacts, that tend to burn out. I replaced the thermostat , then installed a slave mercury relay (contact rating 25A at 240 volts AC),(controlled by the thermostat) to switch the actual load of the heater. The relay started to over heat and latched up. Replaced the merc relay with a "BDR" contactor (big darn relay) with contacts rated at 30A 240 volt AC. Everything works fine, except the relay contacts arc when the relay operates and releases. Question is, how do I stop the arcing. The current measured with an amp meter at the heater is 22 amps . I was thinking of also using a 40 amp 600 volt Triac, any opinions.