TP-351A Potted HSI Circuit Board

The TP-351A is a potted Mark 17DU-117 hot surface ignition (HSI) circuit board built for 120V, remote flame-rod-sense burner control boxes. It runs the full ignition sequence on the heater: it energizes the hot surface igniter, opens the gas valve on schedule, then switches to flame-rod rectification to confirm the burner lit. If the flame signal is lost while the heater is calling for heat, the board automatically resets and retries ignition; after repeated failed attempts it locks out on safety, same as the direct-sense boards used elsewhere in the lineup. There is no field-adjustable set point on this board; ignition timing and flame-monitoring behavior are fixed at the factory.

Fits the remote-sense DX, DX-2, XTS, XTS3, LS, AG1, and CX/MP family control boxes; see Fitment below for the full model list. The TP-351A cross-references to Fenwal part 35-755900-009/2020-91 (also listed as Mark17DU-117, 1FYA7, and 6034083). Confirm the alternate number against the unit's nameplate before ordering, since board revisions have carried more than one Fenwal number over the years.

It ships as the board alone. A TP-390 adapter is required when installing it in place of an older circuit board that used a different harness connector.

Before swapping the board, shut off gas to the heater and disconnect electrical power at the burner control box. Remove the wiring harness from the old board, install the TP-351A with its top mounting bolt, and reconnect the harness through the TP-390 adapter where the original board required one. A qualified service technician should verify normal ignition and flame-sense operation before returning the heater to service. Full step-by-step instructions and wiring diagrams: TP-351A installation sheet.

Specifications

Cross-Reference & Fitment

Documents

• TP-351A-install.pdf (install)