Vaillant EcoTec Plus combi issue - VL-RL Spread too big

Hi All, I am experiencing a simple problem after trying to re-start my Vaillant combi boiler after draining the system. The problem only occurs with the hot water demand and it appears to relate to a VL-RL Spread (error S.53). What is VL-RL spread and how can I ensure sufficient water flow in the boiler. The Central heating side works OK and the hotwater is where the problem arises.

Any help is most appreciated.



S.53 - Appliance is within the waiting period of the operation
block function due to water shortage (VL-RL spread too
big)

Is the auto air vent cap loose?

Did you bleed the air from the boiler using the test program detailed in the manual?

You need to check that the F & R thermistors are fitted securely to the respective copper pipes in the boiler, on a straight bit of pipe and not on the concave section so they are not making contact with the copper properly. Several left the factory incorrectly assembled