Vaillant THERMOCOMPACT VC GB 242E Please Help!

[bananaman123]

Hello Folks

Hope you can help me?

I have a Vaillant THERMOCOMPACT VC GB 242E

The control panel is a Lifestyle LP722

Unfortunately Packed up.

Symptoms:

No light on the boiler Rocker Switch in ON position.

If I remove the 2A Time Delay Fuse on the right hand side and insert it back in the boiler seems to momentarily come on for approx 1 second then turns off.

If I set the LP722 timer to ON on the heating dead nothing.

If I set the LP722 timer to ON on the water I hear (likely a pump) activate but no heating.


The history of the situation I am in.

Called local plumbers (whom are friends of mine) who were very quick to respond ie last night (after work) and helped me go through the basics such as getting the pressure to the correct level. checking all the fuses (i had already done this but no harm in a re check with an experienced eye). we checked the motor was spinning and he said all the obvious things seem to be working. suggested it is likley something BOARD related but could not guarantee this statement without further investigation.

The idea of the late night appearance was to try and help me if it was something obvious unfortunately it appears not. They can of course fix this issue but it needs booking in properly and right now they are MAXED, there are a lot of very RICH demanding clients around gloucestershire demanding their time paying a LOT more money that I have so im sure you can picture the scene .

Ideally on the basis we have no heating or hot water atm I thought i might ask on the forum and see if someone can spot anything that might help?

A bit about me I have limited experience with boilers but do have a lot of experience with electronics down to a design level and also have sufficient soldering skills + equipment.
Anything on the electronics side I can TEST, desolder, what ever you need me to do. I am also pretty good with tools etc.

I am willing to listen to any advice anyone may have.

YES i do understand the risks of messing with gas related equipment but I think in this case it might electronics so possibley something I can do. Even if its not im happy to have a go if its defined as not too risky or silly.

From the advise I was given I have already pulled the board out which is a motherbaord consisting of x3 modular modules. Broken down as follows:

Likely to be the following part numbers. I have IDed the boards using Ebay listings as a guide so please forgive any errors or mistakes.

Motherboard - PCB130241
Fan Module - PCB130451/130395
Flame Supervision - PCB100555
Electronic Regulator - PCB252957/252958

I of course have no experience of this board but can spot any obvious signs of issues.

My attention was drawn to the Fan Module PCB where by the RELAY K3 had accessive carbonisation. Likely caused from long term switching and eventually arcing. I desoldered this RELAY and cleaned it up, cleaned up the contacts etc. Then tested using a 24V lab PSU with a 1K resisitor across the switching coil. relay fired up fine and noticed about 5ohm across the load line. so resoldered hoping that might fix it. Whilst I was at it I re capped all the solder joints incase of dry joints etc and momentarily blipped out the components populated on the board such as the x4 transistors, x5 signal diodes, x4 1N4007 diodes, x2 other relays, rectifier, x2 220R power resistors. the caps i just tested for shorts did not desolder due to time. however this board is LIKELY now in good shape. unfortunately re plugged still same symptom.

Motherboard, Flame board and Electronic Regulator still un tested. no obvious signs of damage.

The plumber that came round last night commented there was no spark perhaps my attention should now be drawn to the Flame Board? looking at these boards they are pretty simple and even without any knowledge of their functionality I reckon I could test it down to a component level IF REQUIRED. Of course we all value our time so wish to avoid any unnecessary testing etc.

anyway thats where im at. I hope someone with a LOT more experience with boilers than I have might be able to point me in the right direction. Or at least make some suggestions.

im all ears. many thanks.

 

[Agile]

Boilers operate as a composite machine under the control of the electronics.

I am surprised you did not replace the relay as 5 ohms measured on the contacts could become far higher if current is drawn.

Your boiler is a relatively complicated one and no circuit information is available for the PCBs.

So it will be possible in theory for you to find the fault but I expect you will find it quite time consuming as you have to trace out every part and test its operation.

Tony

 

[bananaman123]

hello tony

thank you for your reply.

"I am surprised you did not replace the relay as 5 ohms measured on the contacts could become far higher if current is drawn."

I take your point I can of course replace the suspect relay np. I suspect Rapid, RS, Farnell or Ebay will come up with the ones we require.

but.. before i do this:

From the symptom described would you say it "sounds" like a board issue?

plus also if you think it is a board issue do you think the K3 relay on the FAN MODULE board would be the potential cause of the issue in hand?

of course replacing all the relays at this point is the ultimate solution as with all electromechanical components they have a shelf life. However, my first plan is to try and fault find the exact issue prior to house cleaning if you catch my drift.

"Your boiler is a relatively complicated one and no circuit information is available for the PCBs."

Point taken about the boiler.

The boards in terms of electronics > from a component count perspective they are relatively small, its modular so nice and easy to get to, plus its "through hole" not "SMD"(bar the 2" square on the regulator board) so no microscope or heat guns needed to get stuff in or out. The component footprints are really spaced out so access is MEGA easy. there is no silicone splurged all over the place like with a lot of chinese electronics, good quality solder + components have been used, the tracks and pads are nice and big, the components are soldered leg straight so not locked in with legs bent, plus the holes are over sized so the components once desoldered almost drop out. In terms of board level repair it doesn't get much better

I guess my main questions are:

Does it sound like a board issue?

If so are there any checks one can do to try and narrow down which board?

hope you dont mind the further questions.

kind regards and thanks for taking your time out to answer my help request

 

[Bunnyman]

Tony stop talking... Your first test is simple electrics, First switch clock an stats on, do u have 240v l-n, then 240v n to 3. If yes then have you got 240v n to 4.? Let's prove all external controls before u start delving in the pcbs, post back, the older vc has an inherent fault with dry joints on the back of the mother pcb where the red rocker switch is

 

[bananaman123]

hello bunnyman

thanks so much for your for your reply.

Actions as requested.

"First switch clock an stats on"

Stat fully clocked to 30oC, Clock set to Heating ON, Water ON.

for some reason this time I noticed when setting JUST heating on the fans etc now come on. previously it was only doing this when setting the water to ON. Perhaps this is a dry joint and during messing around with the board I have dislodged something?

also the yellow and the green neon lights are ON. if i am honest i cannot remember the status of these previous.

Left this on for a while Pressure fine TEMP 0oC.

"do u have 240v l-n"

YES

"then 240v n to 3."

just to be sure i am getting this right. meter from main incomer N to the relevant pin in this case 3. if this is correct then N>3 is 240V AC.

"have you got 240v n to 4.?"

again if my understanding is correct then N>4 is 240V AC.

"Let's prove all external controls before u start delving in the pcbs"

Second this!

"the older vc has an inherent fault with dry joints on the back of the mother pcb where the red rocker switch is"

We opted not to look at this until we hard back from you after publishing the results but armed and ready to re haul the board out and tackle this if necessary. Might be an idea to just re cap the joints anyway but I await your next suggested move.

THANK YOU !

&

kind regards

 

[bananaman123]

just wondering if anyone had any more suggestions about this? I might have a go at checking for dry joints on the motherboard.

 

[Bunnyman]

If u have yellow and green lights on the pcb the boards are calling for power? If they are on that usually proves the pcbs have gone through their sequence an there should be ignition and burner lights? Is it locking out and popping the black button out on the front