Worcester Bosch 280 RSF(domestic water problems)

12 May 2004
Reaction score
United Kingdom
My Worcester Bosch 280 RSF boiler works perfectly on central heating and hot water.Problems occure when running the bath water,the water flow is ok but turning the hot water tap off sometimes makes the Overheat Thermostat trip.I have done all the Fault Finding tests but because its an intermittent fault I've so far found nothing wrong.The 3-port diverter valve however leaks from the motor shaft,does anyone know if there's a service kit available or at least a cheap supplier?Any ideas would be appreciated.
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Did you have any success with your problem . My 280 is doing the same. I have had both H/ex changed but still get the same problem. :cry:
If your boiler overheats only AFTER you turn the tap off then it has to be the flow switch sticking, easy to clean out as the paddle is inly held in by a large plastic grip, obviously turn off power and water first (its the housing that blocks up so clean out in situ useing smal hard brush or simaler. The diverter valve is available at about £50 but a b...... to change if leaking as the rust can get a good hold onto the plastic body and steel pins. Shaft on the diverter valve to leak ,its usually the midle port cracked.
Thanks, what if it cuts out whilst the hw tap is still on?, could it be the pump no circulating properly?
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If the pump runs slow on the 280 the burner usually drops out before it gets to overheat but if it overheats when on dhw then its prob poor circulation in the water to water, hard to test on a 280 but if you have a poor temp rise say less than 30 deg C at 10lt per min then it points to the water to water £225 including labour
Already changed the water to water, could it be possible that any of the internal pipework in the boiler that runs from the pump and diverter valve could be sludged / scaled.
Finally resolved the fault. It would appear that the pump was getting too hot and seizing. Changed pump and no more problems :p
The Overheat Thermostat tripping fault on my boiler was caused by the fan siezing
So it was just a simple pump-fan-hex--or flow switch fault straightforward, :D

Thats the way I like'em, some were pretty recent aswell only 7yrs back :eek:

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