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I turned ch off a couple of months ago for the summer. Hot water was ok after that until I tried to put the heating on again. Heating would work for half an hour, then warning light would flash rapidly, and both hw and ch would fail. The only way to get the boiler to light after that was to turn off at mains for about 20 mins, then try again, but without ch. Since then, the problem has worsened, with the light coming on and flashing without attempting to put heating on. Sometimes the system runs ok for hot water for a couple of days, but more often than not, it fails after a couple of minutes. The boiler is about 2 years old. Any ideas?

if you have the boiler instructions look in the fault finding guide, the flashing light normally has a sequence to tell you the fault (the number and quickness of the flashing light) sound like its going to flame failure, this can be electrical, a problem with the gas supply or something simpler like the flame sensing electrode.

Almost impossible to diagnose without seeing the boiler. Will watch for your reply if you find out what the fault finding guide says.

Hello, thanks for the reply. I do have both the users manual and the more extensive engineers manual, but can't find either! I downloaded the short booklet, it describes 2 ways for the warning light to flash: Once a second, for boiler overheating or ignition lockout, or as is most probably the case with my boiler, 5x a second ( it's difficult to count that fast!), indicating an airflow fault. Electricity to gas valve will be interrupted if controls don't detect correct airflow. I have noticed that the radio crackles sometimes when the boiler is faltering, and that even when there is no demand ( c/h off, taps off, but in the few minutes following hot water demand), the boiler tries to re-ignite. This is consistent with the advise in the manual, which indicates that the ignition will try to re-ignite after 5 minutes. The engineers manual is much more thorough, offering a menu-type diagnostic chart, but frankly, I found it a bit daunting. I'll keep looking though, I really don't want to pay Bosch £150 for a callout. Thanks again.

...a pattern has definately established itself...when I get up in the morning and turn on the hw, no ch, the radio crackles with electrical interference, and the boiler fails. In order to get the hw to work, the boiler must be turned off at the mains for some time.

Hi, have had this recently with same model, although heating was off for summer the boiler would not light reliably, fault traced to low pressure on heating. The pressure gauges are not very accurate (cheap & nasty), I put some more pressure in system until gauge showed just under 2 bar & away it went!
The method of recharging involves the use of the key stored inside the bottom removable panel, see hand book for use, it basically goes into a valve under boiler and you use a rotary black knob next to it to add pressure, If over done then open bleed screw on a rad to reduce,
I think thats it but I am only a leckie fault finder not a plumber/htg eng,
regards SPARX

An airflow fault is a problem with the flue, fan or air pressure switch. Knowing abit about boilers would help. If you turn the heating on can you hear the fan ? or can you hear a buzzing noise ? if its buzzing the fan could be getting stuck, sometimes can be freed.

If the fan is running it may not be running at high speed or enough to operate the air pressure switch. OR the air pressure switch could be faulty.

As these are room sealed appliances the outer case should not be removed by anyone other than a CORGI registered gas fitter. So it wouldn't be right for me to ask you to remove the boiler case.

I would call a heating engineer out, try someone that works outside of their full time job, to diagnose the fault should only cost about £45 (thats all I charge), if it cant be repaired you will need to pay for parts and labour.

I had the same problem! Traced the fault to a relay on the pcb board,
you will see 3 relays together 2 thin white ones and a orange one
its the middle white relay Tyco v2309-A1024-A802 6A/250V 24V!
Sourced a new relay from a electronics shop for £12.60 fitted new relay boiler now working perfect!
Or you can just get the whole pcb board replaced?

I have the 28i model. And yes it's always been the relays. Although I have been replacing both the thin (Miniature ones). I found out when I had a Bosh Engineer who connected laptop to PCB and said it's the circuit board. I had about 4 PCBs replaced before I asked the guy what part is it that's at fault within the PCB - he told me it was the relay (thin ones) but never told me which one. So I now had 4 old PCBs as I always ask to keep them. I searched and found the relays costing less than £3 so I bought a few and I always replace both just in case. Although I do think it's the middle one (the one between the larger Orange one and slim white one). Theses relays only last about a year BUT saying that so did the stupid PCB! At least it's cheap enough with parts. Another thing to do is to spray the fan (near top right side) with WD40 spray since once the Engineer did that as well to fix problem BUT fault came back and new fan was fitted BUT fault came back and GUESS what - yes it was the relay! I am now looking for a very good quality relay NOT VERY EXPENSIVE one since that does not mean it is any better! I know quite a lot about Electronics and so usually know what is good or bad. The ones I have now know are just of a poor quality but they were very cheap.

Hello,

I've also got the 28i Junior, and after doing quite a lot of diagnostic tests, and reading elsewhere on the web, I'm fairly certain I've got the same problem with the PCB relays.

I searched Google for 'Tyco v2309-A1024-A802 6A/250V 24V' but couldn't find an obvious supplier.

Presumably other manufacturers make equivalent relays. Can anyone tell me where I can buy them?

Thanks,

Piers.

Hello,

Just to let anyone know for the future, I ordered a V23092-A1024-A302 from a supplier on Amazon, for just over £9. The relays are made by TE Connectivity / Schrack.

Noone seems to have the A802 relays in stock, but from inspecting the technical datasheet for the V23092 series, the only difference between the A302 and the A802 is the metal used in the contacts inside (A302 = AgSnO2, A802 = AgNi 90/10). I guess time will tell whether this makes any difference.

For reference, putting it simply the problem was that the fan would not run on high demand settings. Use the CH only, and keep the temperature guage set to a minimum, and it was usually OK, but turn on a hot water tap or set the CH temperature too high, and as soon as the fan sped up past a certain point it would cut out. The gas would keep burning for a few seconds, but without the fan extract running flames would then lick round the outside of the combustion chamber (towards the air pressure sensor), until they got cut out as well.

In the course of diagnosing the problem, I did find that one of the pipes to the air pressure sensor had quite a bit of crud in it, so cleaned that out as well.

Anyway, thank you to all the previous posters, who gave me the knowledge / confidence to fix this without paying a foirtune to an engineer.

Piers.

Piers66 wrote:Hello,

Just to let anyone know for the future, I ordered a V23092-A1024-A302 from a supplier on Amazon, for just over £9. The relays are made by TE Connectivity / Schrack.

Noone seems to have the A802 relays in stock, but from inspecting the technical datasheet for the V23092 series, the only difference between the A302 and the A802 is the metal used in the contacts inside (A302 =

Could you please help?
I tested the relay you mentioned on PCB, it's 3.19K ohms, how about yours?
are those Relay faulty?

carpman wrote:I had the same problem! Traced the fault to a relay on the pcb board,
you will see 3 relays together 2 thin white ones and a orange one
its the middle white r

Hi, Please help: How can I test the relay, I have just soldering the relay off the board.

rjdesigns wrote:I have the 28i model. And yes it's always been the relays. Although I have been replacing both the thin (Miniature ones). I found out when I had a Bosh Engineer who connected laptop to PCB and said it's .

Hi, please help me, do you know how to test the relay, I have solding it off the pcb. I test the resistance 3.19k ohms....

appletree wrote:

Piers66 wrote:Hello,

Just to let anyone know for the future, I ordered a V23092-A1024-A302 from a supplier on Amazon, for just over £9. The relays are made by TE Connectivity / Schrack.

Noone seems to have the A802 relays in stock, but from inspecting the technical datasheet for the V23092 series, the only difference between the A302 and the A802 is the metal used in the contacts inside (A302 =

Could you please help?
I tested the relay you mentioned on PCB, it's 3.19K ohms, how about yours?
are those Relay faulty?

Hello,

The tech spec for the relay says that the 24V version has a coil resistance of 3390+/-10% ohms, so that sounds about right.

The thing is that the failure mechanism is probably in the mechanics of the high voltage part of the relay. I guess you could test it if you had the right gear.

I'd done the other electrical tests listed in the service manual, and given the symptoms and what I'd read online, took a chance on it being the relay at fault. I didn't actually know it was going to work, but it seemed highly likely (and it did!).

Piers.

Piers66 wrote:

appletree wrote:

Piers66 wrote:Hello,

Just to let anyone know for the future, I ordered a V23092-A1024-A302 from a supplier on Amazon, for just over £9. The relays are made by TE

The tech spec for the relay says that the 24V version has a coil resistance of 3390+/-10% ohms, so that sounds about right.

The thing is that the failure mechanism is probably in the mechanics of the high voltage part of the relay. I guess you could test it if you had the right gear.

I'd done the other electrical tests listed in the service manual, and given the symptoms and what I'd read online, took a chance on it being the relay at fault. I didn't actually know it was going to work, but it seemed highly likely (and it did!).

Piers.

Thank you for your reply, do you mind test your removed relay resistance?
I guess the the coil resistance doesnt guaranty the relay working.
whatever I have ordered 3 relay this afternoon