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Posted by on May 3, 2011 in Boat Maintenance, UK, US | 1 comment

Water Heater Relief Valves

Is the relief valve on my boat’s water heater anything special?

Question: My boat is equipped with a water heater that has a brass or bronze pressure relief valve on it that looks just like the valve on the water heater at my house. Can I just pick one up at the local plumbing supply house, or is there something special about the one on my boat? I need to replace it because it has started to “spit” water occasionally.

raritan-heater

The pressure relief valve is the bronze colored device in the upper left corner of this Raritan heater.

Answer: Excellent question.

Land based heater relief valves are calibrated to 150 PSI. This is far in excess of the design parameters for the components used in a typical marine water system. Although the valves look identical, the unit for boats should be rated at no more than 75 PSI—much, much lower than the unit at your house. Unfortunately this fact has been lost on some of the water heater manufacturers that supply the boating industry. I’ve found more than a few that use a land based relief valve rated at twice as much pressure allowed for marine use.

Raritan makes these recommendations about their heaters for marine applications:

  • If the valve is dripping, the rubber seal in the pressure relief valve may have failed with age. The Raritan replacement part # for the new valve is: WH3 and the price is about $26. All the major marine vendors like West Marine or Defender Industries have Raritan parts available.
  • The pressure relief valves used in Raritan water heaters are set for 75 PSI or 210° F. If water temperature or pressure inside the tank exceeds these limits, the valve will unseat.

If engine coolant is used in a Raritan water heater with a heat exchanger, some of the engine coolant may have to be diverted via a bypass valve to insure that the water in the tank does not exceed the limits of the pressure relief valve.

—Ed Sherman

1 Comment

  1. You sure don’t want one of those to blow. Just watch the episode of Mythbusters where the relief valve didn’t work. Amazingly destructive.