Worcester Bosch Boiler Keeps Shutting Down.

Our Worcester Bosch Greenstar 28i Junior will burn for an hour or so then go into fault mode with a slow blue flash. It will reset but then shut down again. Has anyone had this problem?

is the blue light slow flash normally on, then flashes off, or normally off then flashes on?

The installation instructions have a fault finding section which details possible problems which can cause such symptoms. if you haven't got them, they can be downloaded from the Worcester site. Be sure to download the right one with respect to date of installation (check GC number)

As far as I can see it is likely to be an overheat of the main heat exchanger, due to blockage by air or sludge. Or a faulty thermistor. Or a dodgy PCB.

What does the pressure gauge say when cold(1-2 bar)? Does it increase (>3 bar) when it shuts down?

As above, could be a few things. I had a similar issue with a villa not and took me a while to figure it out. Turned out to be a perished seal on main heat exchange which caused a drip when system was hot. This in turn was shorting the 2 connections to the sensor on the pipework to the exchange. £2 for new seal and was fine from there on.

its either ignition lockout, flue overheat or heat exchanger overheat. need more detils on its exact flash pattern (mostly on or off), and what the pressure is to start with

Thanks so much for your help with this one guys. The blue light is 'normally off' then flashes on when in the fault condition. I 'topped up' the pressure to 1.5 bar when cold and it was nearer 1.8 bar when the system was quite hot. (can't be sure where it was when it shut down but suspect under 3.0bar). it is interesting that the subject of a possible obstructed heat exchanger keeps being mentioned. Is this straightforward to bleed? Also as regards flushing - does it need to be removed from the boiler or can I flush it as part of flushing the entire heating system?

regarding the flashing blue light, when it is in the fault condition;

is the light mainly off, then flashes briefly? off off off on off off off on..
or is the light mainly on, then goes out briefly? on on on off on on on off..

pressure seems fine, 1.5 to 1.8 bar is ok

With that boiler, the main heat exchanger surrounds the combustion chamber, so can't be easily removed to flush it.

I assume that the warranty has expired. How old is it?

nothing wrong with the heat exchanger. its ignition lockout. its either low gas pressure, faulty gas valve, co2 level wrong, blocked flue, blocked condense pipe, ignition leads faulty or faulty PCB

Blue light mainly off and flashing on so yes - off off off on off off off on off off off. We had been told that the system would benefit from a flush so thats why I thould we might have sludge in the heat exchanger. A gas fitter who prevouusly attended told us the gas pressure is ok. As regards the gas valve coil a resistance test is mentioned. Will this be conclusive? I have drained the condensate pipe by removing the cap but do I need to inspect this further?

The instructions I have for that boiler with those light flashes say;

"

Gas present and at correct pressure.

Combustion CO2 level.

Flue condition.

Ignition electrodes / harness / connections.

Gas valve (coils 140-190Ω) / low voltage harness connection.

Otherwise replace control board."

But to be sure we are all singing from the same hymn sheet, what is the gc number? it should be on the sticker behind the flap

ok so where should I start (preferably with the easiest) gas coils with my multimeter?

You could start by answering gc number and year of installation

ok GC Nr 47-311-87 N. G. 7716130142-008 0008460

year - 2012

Evan said:

ok GC Nr 47-311-87 N. G. 7716130142-008 0008460

year - 2012

Click to expand...

Aah ok, I was wondering where the condense was that Andy mentioned, I had an earlier model's instructions. I have the right instructions now;

"

Gas present and at correct pressure?

Gas valve

– Check that there is 35V d.c. to each solenoid

– Check the resistance of each solenoid:

Top solenoid = 380 Ω ・} 10% (342 - 418 Ω)

Bottom solenoid = 190 Ω ・} 10% (171 - 209 Ω)

Combustion CO2 level.

Flue condition.

– Blocked flue?

Blocked condensate pipe or frozen condensate.

Gas valve adjustment.

Ignition electrodes/harness/connections.

– Check for condition and resistance of leads

(approximately 2100 Ω)

Otherwise replace control board"

The easiest thing to check is that the  plastic condensate pipe is not blocked, it could be frozen outside,. See if you can disconnect it at the boiler and blow down it.

One thing we have noticed is that when the boiler is cold it will burn away happily for an hour before going into fault mode. once reset while still hot it will fault again very quickly. So it would appear there is a link with the heat of the thing. Could this pinpoint the fault any better?

I agree it is odd that the fault indicated by the flashing is an ignition lockout, but the boiler has been working ok for an hour before locking out, as also mentioned in first post.

Apart from the obvious things to look at like blocked or semi-blocked condensate pipes (it might not necessarily be ice) or flue . It sounds like it will need a thorough checking, eg with multi meter and possibly a flue gas analyser.

Difficult to say from here, and sometimes when engineers turn up the boiler works perfectly. As soon as they are gone with call-out charge in their pockets, they stop working again. Might be an idea to run the boiler an hour before the engineer arrives, although check this with him/her first.

If you need to call out someone, call Worcester.... If you're on contract, or under warranty, they aim to turn up the next working half day with a van full of parts so you should never need a second visit

Thanks again for all your help. WB came out today and found a perished flue balancing hose. This caused high and excessive co and co2 levels. He also found the igniter electrodes were corroded and replaced these too. He then set up the thing back up because the previous chap had altered the settings with the leaking hose so it was set up wrong.

Glad you got it sorted,,,,, thanks for the feedback