Webasto Thermo Top C coolant heater has stopped working

Ian Robinson · Jan 22, 2018

Hi, looking for some advice on my engine coolant heater please.

The coolant heater has not worked the last couple of times the temperature has been below 5c. Fuel level and battery all OK and alternator working at 14.7 volts.

It was working fine earlier this winter, with noticeably quicker (more than twice as fast) heat up when below 5c compared to when temperature was 6 or 7c. I could hear the fan going and the metronomic sound of the fuel pump and slight whiff of diesel smoke outside (but no visible smoke).

But last couple of cold mornings - nothing - no sound at all, and van takes noticeably much longer to warm up.

My 3.5 year old van is now just outside of the 6 month 2nd hand warrantee that I had, and as I say, it was working originally when I bought it.

I have read that the heater can lock-out if it fails to start on 3 separate occasions. Our fuel did run below 1/4 tank recently, so maybe that has caused it to fail to start and now lock-out?

Short of going to my local dealer, does anyone know how I might reset the heater? On line I can see a procedure if you have a control panel or remote for this heater, but my SE only has direct control and remote for the parking heater. The coolant heater is fully automatic (or at least it was fully automatic!)

I was thinking of buying a Carista WiFi dongle - hopefully it will read any fault codes, but does anyone with Carista know if this also gives you a reset option for the coolant heater please?

Maybe it can be reset by pulling a fuse out? The 5amp fuse in the lower dash fuse board location 30 says its for the coolant heater relay - might this reset the heater? Or is there another power fuse to the relay (as surely the heater draws more than 5 amps?) I have checked this 5 amp fuse and it has not blown.

Thankfully, but not unsurprisingly (as it runs off different power source, and has its own controls and fuel pump etc) the parking heater still works, so I can still get a head start on defrosting in the mornings. But without the coolant heater the van struggles to get to full temperature on a school run and this can't be good for the engine, and so for now I drive round the block a few more times to get oil etc fully heated up - but not very fuel efficient!

Any help most appreciated - I have read through many coolant heater threads on this great Forum, but could not see these specific questions answered

Gazellio · Jan 22, 2018

Whats your mileage on the Discovery 3/4 & Range Rover they start to Coke up after highish miles.

MattBW · Jan 22, 2018

Its one of the things I've often wondered. Mine didnt run all the time when I first got the van from new however that was before I knew that if your tank is below 1/4 it will not fire up.

http://www.vwt4forum.co.uk/showthread.php?t=712137
The fuel pick up for the thermotop is very low in the main diesel tank, and if the outside temperature is below 6 degrees, it will fire up....on engine startup automatically, if youre main tank is below 1/4 it can starve the Thermotop's pump and it will shutdown!, if it does this 3 times in succession, the unit will lock out.
You may of experienced that!, and just happened to fill up before it locked out for the 3rd time.
Block 18 will show the unit as locked if it does happen 3 times, just so you know.
And the 3 times, is based on 3 individual engine starts.

You may need to reset error codes if its failed to start 3 times.

Gazellio · Jan 22, 2018

Yes agree if you let the tank run low and it tries to start x3 (as above) it will need resetting with a code reader.

Ian Robinson · Jan 22, 2018

Thanks for the replies. The mileage is just shy of 40,000 miles and both I and the previous owner from new live in the south east, so the number of days below 5C is possibly only 20 or 30 a year. So hopefully it hasn't coked up yet.

Does anyone know if Carista would read and reset the codes or do I need a full VCDS system to do this?

Obviously if a code reset doesn't work I may need to go to a VW dealer or perhaps a Webasto specialist to have it fully checked and serviced. I'm just trying to avoid the hassle if a simple reset does the job

MattBW · Jan 22, 2018

I just read in a few other places its 11c that it kicks in but I always thought it was 6c.

If you have access to a VAGCOM device you can in theory force it to start to test it. I have one if you are ever near Warwickshire or there is a VCDS/Carista thread for users willing to help out..

I'm not sure if Carista will do it but it may.

Gazellio · Jan 22, 2018

A simple code reader should reset that code (I think) It will not be coked up after 40,000 miles. Hopefully it just needs resetting. The Land Rover one is 6c

Ian Robinson · Jan 22, 2018

Thanks for the offer MattBW of using your VAGCOM device - I'm not going to be near you anytime soon unfortunately.

Thanks for the encouragement Gazellio to clear the fault code. Unfortunately, assuming it is a Lockout, more research from VW forums and the Ross Tech site indicates it's not a case of just clearing the fault code, but also changing an adaption channel - so sounds like a basic reader like Carista may not be able to do the job just by resetting the fault code and I will need to use something that can do adaptions?

Can anyone with Carista confirm that it can or can't do what is stated as a possible solution below please:

Would a generic OBD2 lead and the freeware version of VCDS lite do what I need, or am I looking at an expensive bit of kit for this?

The Ross-Tech Wiki says:-
02251 - Heater Unit Locked
Possible Symptoms: Heater not working, Heater Module refuses to clear Fault Codes
Possible Causes: Fuel Level low
Possible Solutions: When found in Aux Heater module of VW Transporter (7H), unlock heater module by saving a 1 in Adaptation Channel 003, then clear fault codes.

Loz · Jan 23, 2018

Have a search on the web for an independent with vcds? The mytreg.com forum and t6forum has a members with vcds areas where you can search for a nearby member with vcds who will do this for you for beer tokens..

Are you planning to attend any of the meets? You may find a member with theirs with them who will take a look for you.

Ian Robinson · Jan 26, 2018

Update that may hopefully help others in future:-

I got the coolant heater working again first thing this morning (3 degrees C)

The Webasto manual says:-
Reset Heater “Lockout” mode by performing the following procedure:
1) Ensure timer or switch is in the “OFF” position. Turn timer or switch to the “On” position. Remove main fuse F2 (20 Amp), reinsert after 5 seconds.
2) Cycle timer or switch off and then back on once more. Remove fuse F2 once again and reinsert after 5 seconds. Heater should attempt to start after inserting fuse.

As I don't have a timer or switch and don't know where the 20 amp fuse is, I tried the following (I knew the starter battery was well charged, as risk of killing battery with restarts on cold morning!):
1) Started van and waited a few minutes and confirmed that heater was not working, no fan noise, no diesel pump noise etc
2) Turned off van. Waited 30 seconds and restarted.
3) Waited 30 seconds and removed 5 amp fuse 30 in lower dash panel that serves the coolant heater relay. Left fuse out for 10 seconds and put back in. Waited 30 seconds and then turned off engine.
4) I waited about 2 minutes and restarted engine. Waited 30 seconds, then took fuse out again for 10 seconds and then put fuse back in. Then I waited a minute of two and nothing happened, so turned off engine, locked vehicle and waited a few minutes to make sure everything had powered down.
5) When I restarted the engine, within about 30 seconds I could hear the fan/pump going under the nearside of vehicle and about 10 seconds later I could hear the diesel pump! I took then van for a short drive and when I turned off ignition I could hear fan/pump running on to presumably cool down the heater on shut down.

I had removed the fuse once previously whilst the van was running and this did not work. So not sure if I was just lucky or not, but the above has worked.

On the school run later this morning (4.5 degrees C), heater kicked in again and everything warmed up very quickly.

Fingers crossed all is now well again - only time will tell