Thetford N3150 not working on Mains

[Red Shoes]

Hi folks.
This is Mr Red Shoes here, so this techincally is my first post! Herself is still under the weather today.
Whilst she was not feeling great yesterday, I spent most of the day with my hand effectively up the backside of our Thetford Fridge Freezer. The unit had auto switched to Gas and gave me an Error 8 when I tried to force it to use Mains, which is "AC heater current 75% below nominal current". I gained access to the power board through the lower vent and checked for power going to the heater and found nothing. I checked the fuse (what an unhelpful place to put a fuse!) which was fine. This made me think that there was a fault with the power board. I took it out and checked for dry joints etc. I also checked that the relay worked. I was resigned to replace the whole board. On refitting the board, I just tested the resistance of the heater and it was open circuit. So the heater is faulty. But do I have one fault here or two.

Does the power board have enough intelligence to work out that the heater element is faulty quickly enough for me to miss the relay coming on and then being turned off again, i.e. the power board is fine. Just replace the heater. I'm thinking I could probably wire up a light bulb on the heater circuit and see if that comes on. Anyone tried that?

Given that I need to change the heater element as a minimum, how easy is it to replace? I can't even see where the wire goes!

If anyone wants any information about checking any of the fuses or relays I can help. However, my logical (I think so) brain is wondering why I possibly have two separate faults creating the one effect at the same time. Any help would be appreciated.

Cheers,
Mr Red Shoes.

 

[WillH]

Changing the heater element in itself is not a huge task, removing the fridge to get at it may be. If you have clear access it's a straightforward job, otherwise take it out.

 

[XxAnthxX]

I’m not sure if you got the error 8 (nominal current) from the manual.....but heres the flowchart for error 8 if you haven’t got it.

 

[Red Shoes]

Hi,
Thanks very much for the flowchart. I'm sure that the heater is faulty, but I'm still concerned that somehow there's a fault with the power board too. I think I'm going to try attaching a 100w light bulb to the AC heater connections, which would use just under half the current of the heater. If the board is working fine, it should light the bulb and not give an error code. I'll then look to see where the heater goes to and how likely it is to be able to replace it with the fridge in situ. I'm not sure how far forwards I could move the fridge without compromising the seal into the living space.

 

[XxAnthxX]

Red Shoes

I couldn’t reach the 240v heater from the lower vent, it’s about 250mm up, near the chimney.

If the power board is sensing the lack of resistance, which it could be, I’d suggest that I would also sense
the difference in resistance of the 100w watt bulb, if it’s not between 210-270 ohms

As the heater is way, way cheaper than the power board, It maybe a better idea to try a replacement first.

Thetford 633572 Heater Cartridge Amazon product ASIN B078T2TVZB
If it works, job done if not you could either keep it as a spare, or return it to Amazon then continue onto the power board.

You could just plug the replacement in to see if it heats and removes the error prior to any fridge removal.

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[Red Shoes]

XxAnthxX

Thanks. I've ordered the mains heater direct from Caratech, who have been mentioned in these forums before as a good company to deal with. I got the 633573 part, which is higher power AC heater, 220w for the later Thetford models like mine. The blue leaded one above, 633572 is the 12v heater. Not sure why the Thetford flow chart doesn't specify their own part numbers!
When it comes, as you say, I can test the fridge operation, which hopefully will show that the power board is fine (fingers crossed!)

 

[Carolyn and Kev]

Hi Guys..we have just had a similar fault rectified on our truck. Error 10 and 8 and 6 kept coming on. 240V would not be seen and the 12v system would not change over when engine running. Calibre Motorhomes and Caravans came to us and found the 240 v element faulty and also an earth fault! The PCB was checked and the guy found the earth breaking contact intermittently so he traced it back to a break in the loom just before the Sergent Charger ! We decided to have a new earth wire installed and the problem was rectified .
The fridge was easy enough to remove out of its surroundings but the element was a bit of a bugger to change because the 12v element sits above and alongside it stopping the 240v one being pulled out! However..it was done and we were sorted and put on our way.
The faults did seem to come back to the pcb but as the guy stated...But Check the obvious first before you rip stuff off for no reason. Glad he did too! Saved us nearly 300 pounds

Kev

 

[XxAnthxX]

Doh,,,,,,I posted the wrong link from my purchased items....I bought the 12v and 240v elements within 6 months of each other from the same supplier on Amazon.

 

[Red Shoes]

XxAnthxX
Not to worry. One has blue leads the other has black/grey ones, so it's clear which is which. The real error is Thetford not putting their own part numbers on their fault finding chart, so much more useful than knowing the resistance range, interesting though that is.

 

[XxAnthxX]

Yeah, that’s right......I just stopped on my purchase history at the first one I came to.

Somewhere I have a parts list that has all the numbers for the available parts for the N3000 range from the N3080 through to the N3175

I think I have travelled the road your now on already.

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[autorouter]

If the power board is sensing the lack of resistance, which it could be, I’d suggest that I would also sense
the difference in resistance of the 100w watt bulb, if it’s not between 210-270 ohms

Two 100W bulbs in parallel would probably fool it into sensing the correct resistance.

 

[Red Shoes]

Hello All,

Thanks to everyone for your help and suggestions. I didn't get around to trying the light bulb, as the new heater arrived before I had a chance, but you're right, autorouter, two 100w bulbs in parallel would work. And thanks, XxAnthxX, for the parts list.

I fitted the replacement AC heater, inbetween rain showers, and, after finding a safe place to lay it, as it will get hot very quickly, tested the fridge and it was happy. So the power board must be able to sense a work, or not working, heater and turn the power off.
I then just had the simple job of replacing the old heater:
The light coloured tube on the right hand side houses the flue from the gas heater, two electric heaters and refridgeration pipe together with insulation material. The tube unclips by squeezing it together to release the clips to reveal the heaters down in their holes. There is also a screw at the bottom of the tube securing it to the base plate. Releasing that helps!

The cables for both heaters were helpfully cable tied to the back of the coil of pipework to the left. No chance of snipping it, so pulled each wire up with hook and cut them, then pulled the spare end out from below.
Tried to pull the heater out of its socket, but no luck. Saw a little stop pin on heater from below and was able to use a long handled screwdriver and small hammer to gently tap heater out.


Pushed new heater into place.
After making sure that the insulation material was distributed evenly aroung pipes, I couldn't manage to reclip the cover, so resorted to cable ties.
Rather than squeeze the new cables back behind the pipework I let them drop down between the pipework and the side of the van. The cables are heat proof anyway.
I reconnected the new heater into the power board and reassembled it. After a final check I reapplied power to the van and the fridge is happy! It's even making ice cubes now.
It is a bit of a fiddle to do it with the fridge in situ, but comforting that I didn't have to remove any of the seals around the fridge, and only a few cuts on the hands for my trouble!
Thanks again for your help. This is the first major issue we've had with the van, so it was good to have some helpful comments!