Bosch Worcester Highflow 400 keeps failing - help!

[Mags46]

We're getting fed up with a series of boiler problems which so far British Gas have been unable to solve.

Jan 01: heating/hot water had failed. BG engineer reset overheat cutout switch and repressurised the boiler (it had gone low).
Jan 02: boiler overheat cutout switch had tripped several times. BG eng reduced system pressure & repressurised the expansion vessel.
Jan 22: boiler worked fine for several days then started banging when hot water run. BG eng replaced the pump & cleaned the bypass/thermostat tube.
Jan 29: boiler worked ok for a couple of days & then started banging again. BG eng replaced the main heat exchanger & put in 2 lots of fastcleanse as we also booked a power flush for Feb 17.
Feb 03: Boiler stopped producing heat/hot water but NO overheat cutout switches tripped. BG eng replaced the fan & air pressure switch. This worked for about 3-4 hours but failed again, possibly after using the hot water.

BG think there is muck in the system which may be causing the initial problems of overheating and tripping the cutout switch. However tey're currently at a loss as to what has caused 2 fans to fail. Can anyone help/advise?

 

[ollski]

Not sure on your fan fault but would say the dhw heat exchanger and manifolds need replacing when the flush is done as the pwerflush just fills it with all the sludge.

 

[petit_pablo]

Theres a filter in the top manifold too.

The flush should be done on the system, the boiler doesnt flush very well as the pressure gets lost in the heatbank.

 

[stevefixitall]

mags these guys are right the highflows up here round about 8 year old plus are notorius for overheating especially on the dhw circuit due to scaled up domestic heat exchanger, manifold and 6mm bundy pipe next to pump.

best thing to do is yeah get it flushed but ret bg to replace dom heat exchanger at the same time cos if is already bunged no hope in high heaven powerflush machine gonna shift the dirt.

 

[Mags46]

Please don't think I'm having a dig at BG engineers. I think it is probably quite tiresome to try to diagnose a fault that may have had several people fiddling around over a series of visits. And I'm very grateful for any advice or ideas which we can put forward. It's just that the current chap does seem truly at a loss as to what's wrong, such that he's bringing his boss round tomorrow. And I'm just getting a bit fed up with having to wait around in a cold house.

 

[Mags46]

I know that they have definitely changed the main heat exchanger (according to the worksheets I have), not sure about the secondary one bu I will definitely suggest it. Keep those helpful ideas coming please.

 

[stevefixitall]

no not having a dig either its very frustrating with these boilers, especially on overheat

 

[petit_pablo]

Most highflow faults are a pain in the ass. Then once you know what it is, its usually a pain to repair

 

[nickso]

i would say its the DHW h/e too, especially if the primary h/e has been changed. wonder if he checked the pipe running to the rear of the primary h/e from the diverter, classic choke point.

no matter, if he is putting a new DHW h/e in it will all have to come out. i would also check the previously mentioned tube from the diverter to pump. if that or the orifice in the diverter is blocked it may cause the diverter to stick and may overheat if it gets stuck in DHW position.

 

[poxy400]

some times you have to face facts its a mare of a boiler when problems start cut your losses and get a new one because when you think they have fixed it.its only a matter of time and they will be back

 

[Agile]

I do have to agree with the generalities of the replies above.

These boilers will work well on a totally clean system but unless its very carefully maintained to be totally clean these boilers will very rapidly fail frequently.

Some of the initial "fauts" that you listed were just a natural consequence of the system pressure not having been kept up to pressure. Thats a user function, not a maintenance issue!

Taking a detached view, its not unreasonable to say that this boiler can be considered as a "high maintenance" model that requires more attention to keeping it clean and the pressure topped up than any annual maintenance scheme is likely to be able to give.

So as a consequence one could say that its about time it was replaced perhaps with a similar current model like the Highflow 440 or 550. They pretty much fit in a similar space as the earlier models.

Tony

 

[Mags46]

Thanks for all the advice.

The latest is that the fan has been replaced, along with the primary cutout switch (wasn't responding) and the circuit board. British Gas spoke to Worcester who thought that at least the fan problem might be a faulty circuit board so here we are. Currently I have heating (yay, better than nothing but neither myself nor the British Gas chap wanted to try running the hot water until tomorrow in case things went completely wrong again.

A Worcester engineer is coming out tomorrow at British Gas' request, to try and resolve the problems once and for all. There will still be a power flush in a week or so (I will remember to ask them to change the DHW heat exchanger) and we are having a filter system put in as well. The system was all power flushed by British Gas in 2005 when there were problems and annually serviced by them since 2000.

Any other recommendations for new boilers if we have to go down that route? I don't really fancy going with Worcester again unless newer models are easier to maintain and more reliable than this seems to be!

 

[Agile]

The latest similar boilers do seem to be much more reliable that yours and earlier models.

But reliability all depends on a totally clean system.

A premature fan failure indicates a faulty flue!

I have heard of BG refusing to cover a corroded flue under their cover.

Getting a joint visit with a Worcester engineer means BG have given up but at least its likely to get all the problems correctly identified.

Tony

 

[nickso]

A premature fan failure indicates a faulty flue!

how so?

I have heard of BG refusing to cover a corroded flue under their cover.

they cant unless its an open flued boiler in which case its never covered. roomsealed boilers are always covered unless its customer damage or neglect.

 

[nickso]

Taking a detached view, its not unreasonable to say that this boiler can be considered as a "high maintenance" model that requires more attention to keeping it clean and the pressure topped up than any annual maintenance scheme is likely to be able to give.

So as a consequence one could say that its about time it was replaced perhaps with a similar current model like the Highflow 440 or 550. They pretty much fit in a similar space as the earlier models.

Tony

unfortunately i have to agree with that. if you own a 400 or pretty much any of its variants you are on a hiding to nothing unless the system is kept immaculately clean. problem is the design of most 400 systems makes it difficult to put any filters on in a meaningful position.

the 440 was a marked inprovement and i would have one in my house. not seen a 550 so cant comment.