Worcester Bosch Highflow 400 RSF

25 Oct 2011
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United Kingdom

I have a worcester Bosch Highflow 400 RSF which is sometimes not supplying hot water when the heating is also on, when the Heating is switched off the Hot Water fires immediately.

I have changed the water dverter valve and chcked the pressure which is fine.

Can anyone tell me if the water demand light should come on and the boiler should fire as soon as the hot water tap is opened or does the boiler use up hot water in its storage tank first and only fire if extra is needed.

Also does anyone have any idea what might be stopping the boiler firing on hot water demand when the heating is on.

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The demand light will only come on when there is either a heating demand or the tap is opened. Basically when you put the programmer on for hot water it heats the slave tank, when that is heated and you run a hot tap the hot water from the slave tank (this is central heating water in the slave tank) goes around the plate heat exchanger and your hot water is heated by heat transfer. As you run hot water the boiler fires to reheat the slave tank, it can't reheat the slave tank as fast as you can run the hot water so when running large amounts of hot the temp will start to drop. You should get a 40 deg rise over your incoming cold temp averaged over 90 litres. Anyway back to your problem. I've had this before all be it rare and it was down to the pcb. Also the diverted valve on those doesn't work like a regular diverter, it only energises and moves over when a heating demand is on. In hot water mode it will just be in rest position so if the diverter fails the symptoms would be no c/h not hit water. Hope this helps.

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