mgcvk

Hoping Scoobynet can solve the problem. We have a Worcester 35CDi II. Long and short it packed up about three weeks ago, turned out to be the fan motor. Original fan had been in from new, around nine years and had required lubricating a few times but no other problems. We have Homecare Agreement with British Gas so fan replaced no probs and all was well for around a week. This original fan hadn't shorted, just worn out. However, the replacement fan shorted and two subsequent fans have also shorted - copper coil completely black, but no obvious drama, boiler just packs up. British gas have replaced the transformer but fan still shorted. Case has now been passed over to Worcester Bosch. Their engineer changed the circuit board and installed yet another fan today!! Four new fans fried in a three week period. Latest one fitted today lasted only a couple of hours with the brand new circuit board and boiler is dead again which presumably will be the fan. Flu is OK and exits at a right angle not vertical, no dampness in there. It is a complete mystery. Mrs is now getting vexed as she is sick of showering at the gym and me poor bairns are a freezin! I am now adept at having a wash out of a bucket sat in bath.

So any gas engineers on here with any ideas? Surely all these new fans can't be faulty? We don't seem to have any other electrical problems and the main board in the house is very sensitive - a light bulb blowing will trip it. Boiler has never tripped the board. Anyone?

addi monster

iTrader: (6)

fans usualy burn out when they are under load, ie dust debris imparing there movment but 4 fans in 3 weeks is a tad odd,

Mog

If the electrical supply to the fan is constant, the only thing I can think of is a bad batch of fans but Worcester would already be aware of other failures if this was the case.

Mog

mgcvk

The fans seem to be the problem but no-one is aware of a bad batch it seems. I kind of hoped the Worcester Engineer might have a fan from a different batch to the British Gas engineers. Are there any other parts that could be causing a problem? Pump head was discussed but ruled out as couldn't effect electrical supply to fan.

scoobeenut

Is the fan impeller getting stuck when they refit it? If the blades can't turn because the chassis is warped or if they are touching something that will probably burn out the motor.

ALi-B

iTrader: (1)

Has anyone actually put a voltmeter on the mains supply? Because you don't blow bulbs doesn't automatically mean the supply is ok (bulbs can work at high voltages, they just don't last as long - depending on the quality).

IIRC many boilers run the fans at mains supply volts even the modern ones with integrated PCBs.

If the supply is above 250volts then you have a issue and need to call your energy supplier to send out round a techy person and a data logger.

lordharding

iTrader: (1)

Silly question but there is three trip switches
You don't think it's one of those that is tripping rather the fans are packing up
Maybe the fan holder is twisted at an angle and it is catching on the side
Try turning the temperature down to 3/4 rather then 5/6 as when they get older they sort of loose the power basically like an engine wearing out

Mog

If the fan impeller was catching anywhere you would hear instantly you turned it on. Has to be the supply voltage or a bad batch.

BULLITT

You can't test Worcester fans for voltage, most tests have to be dead test (no power on, resistance only). Though i think the cdi II has a conventional fan.

If Worcester have been out to it already then they are responsible to come back and repair under the work guarantee from their initial visit. If its a constant problem, ask to speak to your local BG Service Manager (manager for engineers in your area) explain the situation to them. In some cases we have replaced boilers as part of the homecare agreement..

Also the i wonder if they have checked the wiring going to the fan for any breaks/cuts etc

mgcvk

I'm very happy with the way British Gas have handled the problem although unfortunately the fault so far isn't fixed. I have the mobile number for the local British Gas service manager and he has visited us with the main engineer dealing with our boiler, so no problems there. Everyone is scratching their heads. BG engineer has checked wiring for current etc and everything has seemed fine. Worcester Engineer is back on Tues as we are going somewhere with running hot water this weekend! Presumably wiring will need looking at again as we are running out of parts to replace!

ALi-B

iTrader: (1)

I said test the mains power supply at a socket or spur....not the voltage at fan.

This boiler probably has PWM fan control so it would be pointless testing it at the fan.

njkmrs

Try asking on DIYnot Forum .Usually get good quick advice on there if you ask in the right section.
Its worth a try.

mervil

iTrader: (5)

It's strange that replacing the PCB and fan hasn't sorted it, they normally have a fan speed relay that adjusts the speed depending on high/low burner pressure!

This could be, as said above, a voltage issue, not apparent straight away, or maybe an earth leakage?? Tis a weird one!!

Dedrater

Would it be worth sticking a 1amp fuse in the FCU considering it only need 180 watts, it would at least stop excessive current flowing under fault conditions.

mgcvk

Wiring harness hasn't been changed, don't know if that could be problem. What is the FCU?

ALi-B

iTrader: (1)

+1 Ours is on a 3amp fuse in the spur switch and that really should be the absolute maximum. But its quite easy to fit a 13amp, at the peril/risk of the boiler's electronics.

Could even fit a glass fast blow/antisurge, but it'll probably have them on the PCB anyway - Although thats not always the case as my boiler has a unswitched/unmodulated constant 240v supply directly to the fan unit (Its a electronic DC fan, so has a constant AC supply and only take a speed demand signal from the boiler's main PCB, much like modern cooling fans on cars) and when a short to the fan occured the first thing that blew was the fuse in the spur, all the PCB fuses reamined intact .

BULLITT

Not quite.

The 35CDi II uses a conventional burner & fan, the fan is a single speed unit.

What you're referring to is used on newer condensing boilers that have a zero governor gas valve / pre-mixed burners, though it is the fan speed that dictates gas high/low burner pressure.

mervil

iTrader: (5)

The Worcester I Junior (non Greenstar Condensing) has a fan speed relay on the board which, when faulty, stops the fan from ramping up to high speed when the boiler switches over to HW. When this happens, the burner still fires on high burner pressure and the flames lick up the side of the burner melting the APS! Just saying that it's not just the condensing boilers that vary the fan speed

mgcvk

Still no joy. Tomorrow it is having new harness, fan, transformer and board again and if that don't fix it, who knows!!

ALi-B

iTrader: (1)

+1 the NON condensing WB 30CDi (NOT greenstar) has fan speed control on a 240AC fan. Its speed varys upon flame modulation (which is constantly variable depending on demand, not high/low + constant fan like some).

Should be fairly easy to hear if its getting proper speed control, as it should be on maximum speed when the hot tap is switched on full, and it should idle at low speed for 10-15 seconds after the tap is turned off IIRC (most older WBs had a fan overrun timer to prevent heatsoak).

Although I'd expect the boiler to have a flue-overtemp thermo switch. Maybe thats faulty and not shutting down the boiler, allowing the fan to overheat!?



Bullit, I know: A traditional AC fan is very different in looks and control to a DC brushless fan, both however can have varying speed control. Modern condensing boiler commonly use a DC brushless fan, these are obvious on the WB Greenstars (for example) as you look inside the fan motor it has its own printed circuit board and multiple wires for sensing feedback, demand signal and wires (so lots to go wrong). An old non-greenstar just has a brushless open case AC fan motor and two power wire plus earth (not alot to go wrong).


FWIW, I do have expertise in control systems partly in HVAC and automotive/manufacturing systems. So whilst I'm not a plumber, I do know what works a fan! (be it on a air conditioner, boiler, furnace, air handler or just the radiator/condenser fan in your car) .


For example the greenstar DC brushless fans fail often, not the fan itself , but its internal PCB...this can be repaired just by replacing a 10pence input protection resistor belive it or not...I know as I have repaired a couple of WB DC fans (I didn't re-fit them though, I leave that bit for the gas-safe fitter).