F24 misbehaving?

For some time, there has been an intermittent problem of the HW tap in the kitchen failing to cause the boiler to ignite. Sometimes the water runs hot for a few seconds, but then the boiler shuts down and the water runs cold. This problem has become more pronounced recently.

Also, there have been times when, after the CH system has been running for some time, the 1-auto-0 switch has been switched to 0, and the LED4 light has continued to flash to indicate CH circuit on standby. The burner ( LED1 ) has continued to ignite every 10-15 minutes, running for a few seconds, before switching back to standby. This has continued for up to 2 hours before the standby LED 4 has finally switched off.

Over the weekend, both these problems have become exacerbated. Also, now when the OFF-ON-RESET switch is turned from OFF to ON, with the heating switch at 0, both LED 5 and 4 come on, indicating CH circuit is on. LED 1 (burner) then comes on for a few seconds, but the pressure gauge stays at 1 bar and LED 1 then goes off.
Sliding heating switch 1-auto-0 to 1 causes LED 1 ( burner) to come on every 10 minutes or so. The pressure gauge increases to 1 ¾ bar, and the CH circuit runs for 10-30 seconds before shutting off. LED 4 and 5 remain constantly lit.
Sliding heating switch 1-auto-0 back to 0, LED 4 and 5 continue to light constantly, and burner continues to ignite intermittently.

Is this one for the Heating Engineers?