A.01.21 error code
A.01.21 — Maximum DHW temperature gradient level 3 exceeded
What does Remeha Gas 320/620 Ace floor-standing boiler A.01.21 mean?
Remeha documents A.01.21 for the Gas 320/620 Ace as “Maximum DHW temperature gradient level 3 exceeded”. The boiler may continue operating, but the cause should be investigated.
The code identifies the condition detected by the product; it does not always identify the failed component on its own. Confirm the full code and exact model before ordering parts or attempting a reset.
The Remeha Gas 320/620 Ace floor-standing boiler A.01.21 error code indicates remeha documents A.01.21 for the Gas 320/620 Ace as “Maximum DHW temperature gradient level 3 exceeded”. The boiler may continue operating, but the cause should be investigated. This guide explains what the code means, the symptoms and likely causes, the checks that are safe to make, and when to stop and arrange an authorised repair.
Symptoms you may notice
The boiler displays this code when its controls detect an abnormal temperature difference, rate of change or operating limit. Output may be reduced or stopped.
Common causes
Insufficient circulation, closed valves, pump or hydraulic problems, trapped air, low water pressure, a fouled heat exchanger or inaccurate temperature sensing.
Before you start troubleshooting
Use the display, rating label or product menu to confirm the exact model. Similar-looking codes can have different meanings across product generations and regions.
- Record the complete code before switching the equipment off.
- Check only user-accessible controls, filters and external connections described in the manual.
- Do not open gas, refrigerant, combustion or electrical compartments.
Troubleshooting steps
Check only accessible system pressure and external valves. A commercial-heating engineer should confirm circulation direction, pump operation, water pressure, venting, heat-exchanger condition and sensor accuracy.
Can you fix this error code yourself?
This fault is not intended for user repair. Do not remove covers or test internal components; record the code and contact an authorised technician.
A successful reset is not proof that the underlying issue is fixed. If A.01.21 reappears, note when it happens and give that information to the service engineer.
Reset instructions
Do not reset merely to clear the display. Record the code and correct the cause.
Applicable products and models
Gas 320/620 Ace floor-standing boilerGas 320 Ace; Gas 620 AceCurrent and supportedWhen to contact a professional
Contact a qualified Remeha commercial-heating engineer if the message returns, the boiler is locked out, a safety limit has operated, or checks require access to internal components.
Frequently asked questions
What does Remeha Gas 320/620 Ace floor-standing boiler A.01.21 mean?
Remeha documents A.01.21 for the Gas 320/620 Ace as “Maximum DHW temperature gradient level 3 exceeded”. The boiler may continue operating, but the cause should be investigated.
Can I fix Remeha Gas 320/620 Ace floor-standing boiler A.01.21 myself?
This code is not classed as user-fixable. Record it and arrange authorised diagnosis rather than opening the product.
Should I reset the product after code A.01.21?
Do not reset merely to clear the display. Record the code and correct the cause.
When should I arrange a repair?
Contact a qualified Remeha commercial-heating engineer if the message returns, the boiler is locked out, a safety limit has operated, or checks require access to internal components.