Vaillant Thermocompact locking out

[Shiver Metimbers]

Hi all.

Got a Vaillant Thermocompact boiler about 3.5 years old.

The other day it started locking out. A manual reset would start it again for a few minutes, then it would lock out again (lock out indicator lights up).

My Corgi engineer reckons the lock-out is occurring because the boiler can't sense a full supply of gas, so shuts down.

He's a good chap with a lifetime of experience but admits to never having seen this fault before. After 2 hours of inspection, he suspects it's 1 of 3 electrical panels(?) in the boiler at fault but is not sure which. (Apparently each panel is quite expensive to replace so trialling each could be very costly.)

He's going to try and contact Vaillant for some guidance but given that

[1] He's not sure yet ... [2] It's blinking cold ;-( [3] He might get stuck in some awful automated menu driven answering service from a call centre based somewhere in India ..... :))

.... can anyone help with a suggestion?, or maybe, has anyone come across such a fault with this boiler before?

The only symptom I noticed prior to this fault occurring (which may be a red herring) was an small increase (10% ish at a guess) in the temperature of the hot water on the day before the fault.

TIA for any pointers.

[andrewpreece]

First thing, does it have a diagnostic panel, you know, an LCD display detailing fault codes? If so you can interrogate it to view recent faults ( get your intruction manual out! ). I'm not saying that just because the memory quotes a certain fault that its relevant or even happened ( I've seen a couple of fault codes on my Vaillant that couldn't possibly have happened - "no water" for instance ). Worth looking at though.

Secondly, I did hear that Vaillant had a technical helpline, I sure you can get the number from your brochures or Google for it. I'm not saying they'll necessarily be able to help, but if I were Vaillant I'd keep a database of more common faults to feed back to their engineers/customers. Maybe one of our resident gas engineers could comment?

Andy.

[Ed Sirett]

Before shelling out eliminate the cheap stuff first. Using the service manual look up the fault code. (Lockouts would be overheating or flame failure detection (= no ignition) or non water or whatever.

There is a good chance that the fault is a sensor or debris. It might just be a poor gas supply but the burner pressure is valid from about 2-10mbar and is governed, so it would have to be a non-existing gas supply to cause a lock-out.

If and only if all other causes have been found then try the main PCB. Check the APS as these go down intermittently on this model. The APS can be monitored with one of the diagnostics on the display.

HTH

[Shiver Metimbers]

Thanks to all for the replies.

My Corgi engineer measured the output from the gas valve today. Basically there was none (i.e. insufficient output).

So there is either a fault in that gas valve (mechanical) or the PCB's (1 of 2) that control it.

Seems like I have a pretty expensive choice either way (he recommends I contact a Vaillant engineer who will be able to *try* both parts from the van).

There is no diagnostic panel btw, but by following the sequence of lights on the boiler as it tries to light (and from following the manual ) we have come to the above conclusion.

Thanks again to all that replied and if anyone has any further suggestions to limit the next expenditure, I'd be grateful.

[Ed Sirett]

The supply to the gas valve is in two parts. A mains one which is either on or off. Easy to check. And a low voltage one which operates the modulator (The combi version certainly has this and the non-combi is almost certain to have it aswell).

If the mains in on and the gas pressure is outside of the range between ignition and full (about 2m - 10mb) then there is a gas valve problem. If there is no main on the main valve then its a PCB problem. It'll be the PCB which has all the mains connections on it.