Dometic Atwood Water Heater Pressure Relief Valve | 91604 | 1/2" NPT

Protect your older Atwood RV water heater with the Dometic / Atwood 91604 Pressure Relief Valve. This 150 PSI safety relief valve with 1/2" NPT threading is the critical safety device that prevents dangerous pressure buildup in your water heater tank — opening automatically when pressure exceeds safe limits to prevent catastrophic tank failure. A small part that prevents a very expensive (and potentially dangerous) problem.

⚠️ For Atwood Water Heaters Manufactured BEFORE February 2006 Only

The 91604 fits a specific range of Atwood water heaters. Compatibility is strict and date-based — confirm before ordering:

• Atwood water heaters manufactured BEFORE February 2006
• 1/2" NPT thread connection

If your water heater was manufactured in February 2006 or later, the 91604 is NOT the correct relief valve. Newer Atwood water heaters use a different valve with a 3/4" NPT thread — see the next section for the correct part.

Newer Atwood Water Heater? Use the 90028

If your Atwood water heater was manufactured in February 2006 or later, the correct pressure relief valve is the Dometic/Atwood 90028 Pressure Relief Valve (3/4" NPT thread). The 91604 and 90028 are NOT interchangeable — the thread sizes are different, and trying to fit a 1/2" valve in a 3/4" port (or vice versa) will not work and would be unsafe.

What This Valve Does

The pressure relief valve (often called a "T&P valve" or "PRV") is one of the most important safety devices on any water heater. As your RV water heater operates, pressure builds inside the tank from thermal expansion and external water pressure. The relief valve is engineered to open automatically when pressure exceeds the safe limit:

• Opening Pressure: 150 PSI

Without a functioning relief valve, excessive pressure can cause the water heater tank to fail — potentially violently. Modern relief valves prevent that failure mode by venting excess pressure to a safe location before tank damage occurs.

When to Replace the Relief Valve

Pressure relief valves are wear items that should be inspected regularly and replaced when:

• The valve is leaking at the threads or vent (a leaking valve indicates either over-pressure conditions OR a failed valve)
• The valve has been operating for several years — periodic replacement is preventive best practice
• The lever doesn't operate properly when manually tested
• The valve shows visible corrosion or scaling
• You're servicing or replacing your water heater — a new relief valve is cheap insurance

Manufacturers typically recommend manually testing the relief valve at least annually by lifting the lever momentarily — verifying the valve is free to operate when needed.

⚠️ Professional Installation Recommended

Water heater service should be performed by a qualified RV service technician. Improperly installed pressure relief valves can fail at critical moments, creating serious safety risks. Always test the new valve after installation per manufacturer instructions.

What's Included

• (1) Pressure / Temperature Relief Valve
• Installation instructions

Key Features

• Genuine Dometic / Atwood OEM pressure relief valve
• 150 PSI opening pressure
• 1/2" NPT thread connection
• For Atwood water heaters manufactured BEFORE February 2006
• Critical safety device — prevents dangerous tank over-pressure
• Compact dimensions: 7-1/4" × 1-3/4" × 1-1/2"
• Lightweight: 0.5 lbs
• Backed by a 2-year manufacturer warranty

Specifications

• Brand: Dometic (Atwood)
• Part Number: 91604
• Type: Pressure Relief Valve (T&P)
• Opening Pressure: 150 PSI
• Thread Connection: 1/2" NPT
• Application: Atwood RV water heaters manufactured BEFORE February 2006
• NOT Compatible With: Atwood water heaters manufactured February 2006 or later (use 90028 / 3/4" NPT instead)
• Dimensions: 7-1/4" × 1-3/4" × 1-1/2"
• Weight: 0.5 lbs
• Sibling Part (Newer Models): Dometic/Atwood 90028 (3/4" NPT)
• Warranty: 2-year manufacturer warranty