Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display)
Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) code c: 21: c: 21 (alternating with d: 0/1/64)
The maximum gas or oil pressure was exceeded, which locks out the burner at startup.
Safety first. This code involves a gas, flame or electrical hazard. Do not keep resetting it. Leave burner, gas train and high voltage work to a qualified technician. WERCS answers 24/7 at (877) 489-3727.
- Code
- c: 21
- Name
- c: 21 (alternating with d: 0/1/64)
- Controller
- Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display)
- Type
- General fault
- What it does
- Lockout: the control shuts down and stays off until it is reset
- Risk
- RED Specialist territory
- Reset
- Needs a manual reset
- Source
- The manufacturer's manual (subscribers see which manual and page)
Updated July 23, 2026
How to fix it
Subscribers get:
- What to do next, in plain words
- Which manufacturer manual it comes from, linked
- The 4 common causes listed for this code
- Booking a live video call with Ben, a master booth technician ($250/hr, paid per call)
Questions about this code
What does Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) code c: 21 mean?
The maximum gas or oil pressure was exceeded, which locks out the burner at startup.
Is Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) code c: 21 dangerous?
It is graded red, specialist territory: it involves a burner, gas, flame or safety lockout, so leave the repair to a qualified technician.
How do I fix Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) code c: 21?
The manual's fix and the step by step check for this code are in WERCS Diagnose, plans from $49 a month. For help right now, WERCS answers 24/7 at (877) 489-3727.
Other Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) codes
c: 7 · c: 7 (alternating with d: 0/3)c: 12 · c: 12 (alternating with d: 0/1/2/3/4/5)c: 14 · c: 14 (alternating with d: 0/1/64)c: 20 · c: 20 (alternating with d: 0/1)c: 22 · c: 22 / OFF S (alternating with d: 0 andc: 60 · c: 60 (d: 0)c: 70 · c: 70 (with d: 23 / d: 26)c: 71 · c: 71 (with d: 0/1/2/3)c: 85 · c: 85 (with d: 0 / d: 1)c: 93 · c: 93 (with d: 3)
All 24 Riello RS/E BLU Burner Control (REC 27.100A2 with RDI21 display) codes · Every fault code