Verified boiler fault code
Keston 38 Fault Code (Heat 2)
Blocking delta-temperature supervision fault between flow and return.
Safety disclaimer
Fault code summary
- Manufacturer
- Keston
- Fault code
- 38
- Fault type
- Temperature sensor, Circulation
- Severity
- blocking
- Reset
- The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.
- Applicable models
- Keston Heat 2 45, Keston Heat 2 55, Keston Heat 2 45P, Keston Heat 2 55P
Quick answer
Blocking delta-temperature supervision fault between flow and return.
What does this fault code mean?
Blocking delta-temperature supervision fault between flow and return.
Common causes
- Blocking delta temperature flow/return.
Symptoms
- The boiler fault screen shows code 38 and a blocking condition.
What can the homeowner safely check?
- Record the code and contact a qualified engineer.
Boiler reset information
The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.
When should I call an engineer?
Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.
Engineer diagnosis
- Compare flow/return readings and investigate circulation.
Applicable boiler models
Related fault codes
- 1 — Heat 2
Flow thermistor open circuit (blocking).
Read fault code - 10 — Heat 2
Water-pressure sensor defect.
Read fault code - 11 — Heat 2
Flow thermistor open circuit; lockout after 24 hours.
Read fault code - 12 — Heat 2
Flow thermistor short circuit; lockout after 24 hours.
Read fault code - 13 — Heat 2
Return thermistor open circuit; lockout after 24 hours.
Read fault code - 14 — Heat 2
Return thermistor short circuit; lockout after 24 hours.
Read fault code - 19 — Heat 2
Heat thermistor open circuit (blocking).
Read fault code - 2 — Heat 2
Flow thermistor short circuit (blocking).
Read fault code
Manufacturer documentation
Keston Heat 2 Installation & Servicing ManualFAULT FINDING MENU: Blocking delta temp flow/return — code 38.
Last verified
2026-09-12
Frequently asked questions
What does Keston 38 mean?
Blocking delta-temperature supervision fault between flow and return.
Can I reset a Keston 38 fault?
The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.