BAXI COMBI INSTANT 105E Won't light

[chillyisons]

Hi, This boiler has been problomatic for years with numerous parts being fitted anually Ive lost count of the number of temperature sensors ch and dhw, diaphrams, 2 pressure releife valves, a stuck diverter valve plus a leaking pump but has now completly stoped working. The diverter valve has just been changed and the boiler fired up with excelent results the pre heat heated the water then stopped where as before it heated for a long period to get to the set temperature as it was heating the rads as well. A small leak was spotted at the back of the diverter valve so the boiler was drained and everything was nipped up a little tighter. Now I dont know if the pcb got wet the last time it was drained but the boiler now refuses to light. When switched on the fan spins the pump starts up and the electronic ignition clicks but almost straight away the fan stops and the following two lights flash

30oC - FLAME FAILURE
40oC - SAFETY THERMOSTAT ACTIVATED

There is 240v at the main block and the fuse at the main block in the boiler is fine. The air pressure switch clicks when the fan spins and a contunuity check shows the switch to be working. I have blown through the pressure pipes into the flue (Both the rubber pipes) and they are clear. I have blown through the rubber pipe to the brass fitting in the burner which is also cleare. when the fan and pump initialy spin the pcb shows 240v at its various sockets which is cut as soon at the fault lights come on. We do have a gas supply to the house as the cooker hobs are working. The boiler last drain down was Sunday and the pcb has been remover and checked for dryness since (there were some droplets under the pcb in the plastic control housing. Its now Tuesday and it still wont fire up with what must now be a moisture free pcb. Any ideas on what to test next? Thanks in advance

 

[fixter1]

check o/h stat could be fault on the gas vavle dose the burner light up at all

 

[diamondgas]

Hi Chillyisons,
On many occasions on fitting a new PCB those two lights flash together ... That's bye-the-bye however. Do you get any ignition at all? Does the gas valve energise?

 

[chillyisons]

thanks for answering folks

we have no ignition at all just the clicking of the igniter. its as if no gas getting to that area at all.

will have to ask hubby on the overheat stat!

 

[chillyisons]

hubby checking the o/h stat and says that it is reading across terminals is 0 ohms. the continiuity test shows that it is a completed circuit

plus

the terminals spin around in a circle- is this right?

 

[Billy Bob Bob]

more than likely the pcb has got wet try using a hairdryer on it

 

[diamondgas]

O/heat stat ok ...... Is Mr "Chillyisons" Gas Safe certified? You really don't want to be delving any further. If you know you have a spark at the electrodes and you have 240v at the gas valve solenoid then you'll know how to check the ignition burner pressure I assume?

 

[chillyisons]

In response to the last two posts Mr gas man first... the pcb has had a hair dryer aimed at it on a low heat setting for a good hour or so with no effect on the operation of the boiler. Secondly to diamondgas in answer to your querie I am not gas safe certified and no I dont know how to check the burner pressure nor do I have the equipment to do so. So the stat is ok,the pump pumps breifly on start up the fan starts breifly on start up,the pressure valve in the top next to the flue works (Listing good bits to make me feel better) and I have a good strong spark at the electrode but if the gas solonoid it the one with 2 small black wires with spade connectors on with what looks like the brass bleed nipple (a bit like on a brake caliper of a car) then it reeds 0v when the fan and pump breifly spin up. There is also a multi plug which is secured with a single screw to the gas block which reads 240v briefly during fan and pump spin up, before error code

 

[desrob]

In response to the last two posts Mr gas man first... the pcb has had a hair dryer aimed at it on a low heat setting for a good hour or so with no effect on the operation of the boiler. Secondly to diamondgas in answer to your querie I am not gas safe certified and no I dont know how to check the burner pressure nor do I have the equipment to do so. So the stat is ok,the pump pumps breifly on start up the fan starts breifly on start up,the pressure valve in the top next to the flue works (Listing good bits to make me feel better) and I have a good strong spark at the electrode but if the gas solonoid it the one with 2 small black wires with spade connectors on with what looks like the brass bleed nipple (a bit like on a brake caliper of a car) then it reeds 0v when the fan and pump breifly spin up. There is also a multi plug which is secured with a single screw to the gas block which reads 240v briefly during fan and pump spin up, before error code

get a qualified gas safe engineer to look at it,knowledge is every thing and a lot of qualified people have gone through hard times hours at college etc to gain knowledge, dont expect knowledge to be given over easily, there's a fine line,i'm of the opinion a little knowledge can be dangerous and to answer your problem question,would, in my opinion cost you.

 

[diamondgas]

Secondly to diamondgas in answer to your querie I am not gas safe certified and no I dont know how to check the burner pressure nor do I have the equipment to do so. So the stat is ok,the pump pumps breifly on start up the fan starts breifly on start up,the pressure valve in the top next to the flue works (Listing good bits to make me feel better) and I have a good strong spark at the electrode but if the gas solonoid it the one with 2 small black wires with spade connectors on with what looks like the brass bleed nipple (a bit like on a brake caliper of a car) then it reeds 0v when the fan and pump breifly spin up. There is also a multi plug which is secured with a single screw to the gas block which reads 240v briefly during fan and pump spin up, before error code

Chillyisons, without doubt you prove you are competent with electrics and have done all you can, more than a great deal of 'qualified' engineers are capable of..... However I think you've reached a point where you may need someone qualified to check out the gas components... If your PCB is still staying on two light faults it may well be that it it faulty. They cost around £100 and as a competent electrician you can replace it should you wish. However you can not, legally, interfere with gas valves and the like

 

[chillyisons]

desrob... not a problem if you dont want to assist personaly but the main problem is finding an engineer who isnt just going to turn up and randomly replace parts at my expence until the boiler might work or Im totaly out of cash. I myself went through years of training so understand where your coming from but I give my assistance through forums freely to people such as myself that havent got the cash to just say Ill ring someone and they can do it for me but fully understand limitations and dangers so I will not be touching the gas side myself. dimondgas many thanks for all your help but as you have said I need someone gas qualified to check the gas valve block and other gubbins related to it. I have found some brand new pcb boards on an online auction site for about £100 and swaping it out wont be a problem as its been out and back in for drying and to check for and dry solder joints of which there were none and as you know is a simple unplug replug job. Im just wondering if I should go in with both feet and get the pcb or try to find someone to come out and check the gas side first. I would imagin if the pcb is faulty i'm going to end up paying some one to stand there and say I cant check the boiler properly until it has a functioning pcb thats half an hour plus call out please🙁. Which route would you think is best from here? Would a sticking gas solonoid throw those faults up on the display or is it a 90 odd % sure its a duff board?

 

[Billy Bob Bob]

if the pcb has got wet and in particular if its a Siemens board weird faults can happen,(not seen this one though)so its either gonna be the pcb or gas valve have you checked the isolation valve under the boilers turned on? no chance of it being off but but to check costs nothing,did you take the pcb out to dry it ? in situ water can remain in the facia channel

 

[chillyisons]

I had the pcb out gasman and yes its a siemens there was a bit in the facia but not anymore and I hair dryed it loads. The new pcbs for sale ive seen dont look the same as mine but are listed as being suitable for my model though.

 

[Billy Bob Bob]

yes replacements a Honeywell as your competent with electrics theres a strong chance its the pcb Siemens can not be saved with a hair dryer,sometimes cleaning them in distilled water works and throughly drying but its highly unlikely this will work on a Siemens board again it could be the gasvalve my moneys on the pcb especially if the fault occurred after having water carrying parts replaced,very easy to do this if your unfamiliar with this boiler

 

[diamondgas]

Hi Chillyisons,
I'm virtually sure you can check the gas valve solenoids .. it has two solenoids I believe and they may well be labelled when you remove the molded plug. Don't quote me but I think the it's top two and bottom two if there's five pins. There's that bleedn' many gas valves and derivatives ....... ! However you'd be looking for a resistance reading through both coils and not infinite! That at least will let you know if the gas valve is at fault or not. I'm inclined, to wards the PCB ... nut without being there I couldn't be certain ... If you buy a new one and it's not that it'll do as a spare eh!! lol

Please let us know the outcome ... cheers!

 

[chillyisons]

Morning all! All be it a slightly fresh one... swithched the boiler on this morning hoping the baxi boiler fairy had paid a visit last night but sadly she didnt. Now then I have removed the molded multi plug from the gas block and there are five pins as you mentioned diamondgas. The top two are V2 and read 1.325 ohm constant, the centre pin is earth and the bottom two pins V1 read in the reigon of 1.325 ohm for a fraction of a second before droping straight to 0 ohm and if the multi meter probes are left in contact with the V1 pins it reads a constant 0 ohm. Now for the strange part remove the probes and then make a new contact with the V1 pins results in a 1.325 ohm reading for a fraction of a second before droping to 0 again😕 I have tryed this several times with the same results every time. Does it sound like a strong candidate for a new busted boiler part or is this strange behaviour normal for this component. Seems rather odd to me. Also checked the gas isolation valve which is open as per gas mans request and rather than using distilled water I have cleaned the pcb with solvent based electronic component cleaner but still have flame failure and saftey thermostat warning shortly after the fan and pump spin up then stop.

 

[fixter1]

solenoid packed up should have a constant reading....

 

[diamondgas]

Now then,
Well those readings threw me! I would have thought you'd have given either an infinite reading or a resistance reading a lot greater than you've got. If you haven't already done so try for a resistance between the two outside pins 1&5 and also you could check for 240v between pins 2&4 on the PCB plug 'A1' they're the supply wires to the gas valve. With the readings you've given the fuse to the board should have blown I'd have thought. 30 & 40 flashing still sounds like the PCB!! It's not always an exact science in this job. What tends to happen through time is that we get it wrong on fewer and fewer occasions. I had a new PCB for a 105e I got wrong some years back, fortunately it got re-used later...

 

[fixter1]

if you have 240v to the gas vavle , on a1 between pins 2&4 as diamondgas said gas valve is shot,,

 

[chillyisons]

4.15 ohm top pin to bottom pin is constant reading
240v at 2 and 4 temporarily while fan and pump fire up before fault occurs