This demonstration guide answers one field question about bypass water that overheats in the pump head. Measurements come before parts, and the notes are not a generic equipment FAQ.
Diagnose before replacing parts
Start with discharge temperature during a long bypass. That reading separates bypass water that overheats in the pump head from adjacent faults that share the same complaint.
If the measurement is out of spec, treat the thermal-relief valve as the primary path. If it is in spec, do not replace the thermal-relief valve just to complete a parts list.
Repair the failed system
The usual correction is the thermal-relief valve, installed to the documented spec for this complaint.
A demonstration shop records the finding so the next technician is not repeating a guess about bypass water that overheats in the pump head.
Stop before you make it worse
Do not capping the thermal-relief outlet. That shortcut hides the original measurement and creates a second failure.
If the machine still fails after the thermal-relief valve is corrected, convert the visit to a broader diagnosis rather than stacking parts.
Written and published by Ridgeline Small Engine.