Vaillant F.23: the temperature spread says water is barely moving

What Does Error F.23 Mean?

Vaillant defines F.23 as the temperature spread being too great, or water circulation too low. The boiler measures flow and return temperature and compares them, and when the difference grows beyond what the appliance allows, it concludes that not enough water is passing through the heat exchanger to carry the heat away. Applies to: Vaillant ecoTEC gas boilers covered by the Vaillant United Kingdom fault code list The definition used here is Vaillant's own fault code list for ecoTEC appliances sold in the United Kingdom. Vaillant uses different fault numbering on other ranges and in other markets, and a Glow-worm appliance, though part of the same group, has its own published list. Check the code against the label inside your own casing flap. Owner-safe checks: Feel each radiator after a heating attempt and note which get warm, which stay cold, and whether the cold ones are cold at the top or the bottom. | Check the pressure gauge and record the reading, since a system that has lost water often has air in its place. | Confirm that radiator valves and any thermostatic heads have not been closed off, particularly on circuits recently worked on. Qualified technician: Setting or replacing a pump, venting a sealed primary circuit, power flushing, and testing flow and return sensors are Gas Safe registered tasks on this appliance. | Kettling or banging from the boiler is a reason to stop using the heating rather than to keep trying, because boiling against the exchanger causes cumulative damage.

Other Common Vaillant boiler — Vaillant ecoTEC gas boilers covered by the Vaillant United Kingdom fault code list Error Codes