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Bosch Worcester Highflow 400 no heating no hot water?

We've had an ongoing deries of problems which Brit.Gas are struggling with...
31 Dec: no heating/hot water - felt rather foolish when BG engineer reset a cutout switch & re-pressurised the system.
02 Jan: after system cut out several times (we reset it) BG eng reduced system pressure & re-pressurised the expansion vessel.
22 Jan: Boiler operated ok for a few days then started to bang when hot water run. BG eng replaced the pump & cleaned bypass/thermostat tube.
27 Jan: Boiler ok for a couple of days then banging again. BG eng replaced secondary heat exchanger.
29 Jan: Boiler banging again after 12-24 hours. BG eng replaced main heat exchanger. He also added 2 lots of fastcleanse in anticipation of a power flush booked for 17 Feb.
02 Feb: fan & air pressure switch replaced after boiler switched off (no heat/hot water, cutout switches NOT trippped).
03 Feb: replacement fan broke again. Something inside melted and without the fan the boiler won't operate.

Starting to feel that BG don't actually know what the problem is. They are taking the hit on the power flush financially (we have paid for one before on a service contract) so it's not costing us beyond our service contract. They think there is muck in the system (magnatite) but don't know why the fan has gone twice.
Mags, February 2010
How do you increase the pressure as ours has dropped??

Lee, December 2010
My hi flow also suffers from noise when the hot water side kicks in from cold, ie morning start up, it has a sound best decribed as a 'creaking ship' and this happens for about 2-minutes, it makes a noise then goes quiet in cycles of about 30 seconds, the noise reduces and then goes away.
Sytem pressure is OK, i have replaced the pressure vessel, its had conditioner in the system from new.
If i was a betting man i would guess that either the hot water heat exchanger or the main one was clogging up and the noise i hear is cavitation as the more i increase the system pressure the less it becomes, but i am getting towards two bar and its still noisey, anyone had the same .
Had plumbers look at it but they just chaged thinhs at great expense but never made a difference
any ideas

tony, February 2010
They've already done that. It's quite possible that the 2 fan failures are unrelated to dirt in the system but the engineer thinks 2 fan failures is indicative that 'something else is wrong'. I can't help feeling we're in for a run of them replacing every part one by one.

Mags, February 2010
This can be a difficult problem to resolve. I had a similar problem with the same boiler. Ultimately i replaced the Main Heat exchanger. This resolved the problem and has now been working with no problems for several months.

Henry, February 2010
link Click here to see other fixes for Worcester.