Pentair Tubesheet/Coil Kit 400K Pool | 77707-0234

Pentair MasterTemp / Sta-Rite Max-E-Therm 400 Tube Sheet Coil Assembly Kit (Old Tub Design) | 77707-0234

The Pentair 77707-0234 is a factory replacement tube sheet coil (heat exchanger) assembly kit for select 400,000 BTU pool and spa heaters. It is used to restore heating performance when the existing coil is leaking, scaled, or internally damaged. This kit is intended for MasterTemp 400 (models 400NA and 400LP) and compatible Sta-Rite Max-E-Therm 400 applications where this part number is specified.

Compatibility

• Fits: Pentair MasterTemp 400 heaters, models 400NA and 400LP (where 77707-0234 is specified)
• Also used on: Sta-Rite Max-E-Therm 400 heaters (where 77707-0234 is specified)
• Design note: Commonly associated with heaters manufactured before January 12, 2009 (old tub design). Verify your heater’s parts list to confirm.

What This Kit Does

• Replaces the heater’s tube sheet/coil assembly (heat exchanger section) that transfers heat to pool water
• Helps correct internal leaks, reduced heat output, and performance loss caused by coil damage or heavy scaling
• Provides the required sealing components for proper reassembly (kit contents vary by heater design revision)

What’s Included

• Tube sheet coil (heat exchanger) assembly for MasterTemp/Max-E-Therm 400 applications
• Required O-rings for sealing the coil/tube sheet connection points (as supplied with the kit)
• Insulation components (as supplied with the kit)
• Igniter (as supplied with the kit)
• Blower gaskets (as supplied with the kit)

Common Signs You Need a New Coil Assembly

• Water leaking from the heater cabinet or evidence of internal water damage
• Poor heating performance after confirming proper gas supply, airflow, and clean filter flow
• Repeated “sooting” or overheating symptoms related to restricted heat transfer (often from scaling)
• Visible corrosion or damage to the existing coil/tube sheet assembly during service

Installation Notes

• This is a major heater repair. Installation is best handled by a qualified pool heater technician.
• Verify your exact heater model and manufacturing/design revision before ordering.
• After replacement, confirm proper water flow, combustion airflow, and venting to prevent repeat damage.
• Address the root cause of coil failure (water chemistry, scale, low flow, freeze damage) before restarting the heater.

Related Products

• Coil/Tubesheet Sealing O-Ring Kit (400NA/400LP) - 77707-0119
• Manifold Kit (400NA/400LP) - 77707-0016
• Thermal Regulator Kit - 77707-0010
• Water Pressure Switch - 42001-0060S
• Drain Plug - U178-920P
• Pentair MasterTemp 400 replacement parts
• Sta-Rite Max-E-Therm 400 replacement parts

Maintenance Tips

• Maintain balanced water chemistry (especially pH and alkalinity) to reduce scaling and corrosion inside the heat exchanger.
• Keep flow in spec: clean the filter, baskets, and pump strainer to avoid low-flow overheating and coil stress.
• If you operate in hard-water areas, consider periodic scale prevention practices and monitor heater outlet temperature.
• Winterize properly in freeze-prone areas—freeze damage is a common cause of coil and header failures.