Worcester Bosch [Red light flashing]what it means

Worcester Heat Systems, as the company then was, built a decade of boilers with no display and no code — the 24CDi, 28CDi and 35CDi II, the 26CDi Xtra, the 25Si and 28Si, the 24i and 28i Junior and Si II, the 9-24 CBi and the floor-standing Highflow 400 Electronic. On these the indicator lights do the talking, and Worcester's own user guides give the decode to the householder, which is unusual for them. The CDi and Si have four lights: a green mains light and three red ones for central heating demand, hot water demand and flame.

The central heating demand light flashing slowly, about once a second, is an ignition lockout: the burner did not light within ten seconds and the gas valve has been shut. Both demand lights flashing slowly together is the overheat cut-off. The central heating light flashing fast, about five times a second, is what the user guide calls an appliance fault other than ignition — the installation manual's fail point for it is a sensor. The hot water demand light flashing fast is an air flow fault on a fan-flued boiler, or flue spillage on an open-flued one. The Junior and Si II have a single fault indicator that is also the reset button: slow for ignition lockout or overheat, fast for an appliance fault. The CBi has a lock-out light, steady for overheat and flashing for flame failure. The Highflow 400 Electronic flashes its CH light slowly for lockout, both lights slowly for overheat, both alternately for what Worcester call a fault of a more complex nature, and both fast for spillage.

The reset differs by range and is on this page, because pressing the wrong thing for the wrong number of seconds is why so many of these calls go round in circles. What every range shares is the rule Worcester print in each guide: slow flashes are cleared with the reset, fast flashes are cleared by removing the fault or switching the power off and on, and if it keeps happening it is a service engineer's job.

1. 1

   Work out which boiler you have from the badge and which light is doing what. Four lights with red demand lights: CDi, Si or Xtra. One oval light that is also a button: Junior or Si II. A light labelled lock-out: CBi. Two lights called CH and HW on a floor-standing boiler: Highflow 400 Electronic. Then count — roughly once a second is slow, five a second is fast.

2. 2

   Slow flash on a CDi, Si, Junior or Si II: press the reset button and hold it for five seconds. On a CBi or a Highflow 400 Electronic there is no reset button — turn the heating temperature control fully anticlockwise, to O on the CBi, and back to where it was. On a 24i or 28i RSF, which has no fault light for lockout at all, end the demand: turn the heating knob to the summer position and back, or turn the hot tap off and on.

   Once. An ignition lockout that comes straight back is a boiler that is not lighting, and repeated resets on an ignition fault are not safe on a boiler this age. Call a Gas Safe registered engineer.
3. 3

   Fast flash: do not press anything yet. Look at the flue terminal outside for anything blocking or damaging it, then switch the boiler off at its switched socket or spur, wait, and switch it back on. Worcester's guides say a fast flash clears when the fault is removed or the power is cycled, not with the reset button.

4. 4

   Both demand lights slow, or a Highflow 400 with both lights slow: check the pressure gauge before you reset. The overheat pattern on these boilers is very often a system that has lost pressure or is full of air, and Worcester's first question at that fail point is whether it is pressurised and vented.

5. 5

   Tell whoever comes which light, and whether it was slow or fast. On a CDi that single fact sends the engineer to the right fail point in Worcester's chart before they open the case.