12V Brain fuddler

[Uggers]

I've got a boat that has a 2008ish Truma boiler/blown hot air combo. One that a lot of camper vans use of the same age.

It stopped working a while back specifically sounding like it doesn't ignite. Weirdly trying it by chance during the cold spell in early Jan, the unit fired up and worked faultlessly for the weekend. It has now gone back to the default of not firing up now it's a bit milder.

The weird thing I've found that if I run it from an isolated 12v leisure battery it fires up and runs fine (tried multiple batteries and all good) it's just when I connect it back to the boats 12v electric system (using those same batteries in parallel) it immediately reverts back to type and fails to fire up.

I thought it may have been inadequate wiring to the unit and seeing a voltage drop, so beefed up the wiring to 40A stuff, it still fails to ignite and having a meter on the heater terminals there is zero voltage drop.

I've considered a big 2 pole relay isolating a battery to run the heater when needed, but this means the battery sees no charge in that time so seems a bit of a flawed work around.

Anyone any ideas?

Of course Im also limited by parts as Truma no longer support the unit, but they'll gladly supply a new unit at £1700

[anonymous-user]

My diagnosis and checking would have mirrored yours!

You do, however, mention that the pesky thing fired up as if it were normal in colder weather, is there a thermostat somewhere that is not playing properly?

[Scrump]

I have the same vintage truma unit in my van. Mine is temperamental after I have turned the gas off, after opening tne gas supply it will start but then cuts out. Eventually it will run, but if I leave the gas turned on then it runs perfectly every time.
No idea about the electrical issue, mine is connected to a power management system with two leisure batteries and the van battery connected via smart controller.

[donaircooleone]

Truma C series?

As you've isolated the appliance and supplied another power supply I'd still be inclined to test the original wiring and check for other negative influences. Some appliances can be really funny with voltages especially if you have some misbehaving chargers (not always obvious with a multi-meter).

[Caddyshack]

Is it voltage sensitive? Maybe test the actual voltage you are seeing on the boat - I know you typed that it doesn’t drop but you didn’t say the actual voltage.

I had an issue in our camper, it was in the high 11 volts which some things did not like, I adjusted the solar controller to 13v and everything was then very happy.

[Uggers]

Hi all, thanks for the replies and sorry for being slow to get back to you. I'll try and address most of the comments

JB99 said:

My diagnosis and checking would have mirrored yours!

You do, however, mention that the pesky thing fired up as if it were normal in colder weather, is there a thermostat somewhere that is not playing properly?

It's a consideration, but my thoughts would be it wouldn't attempt to fire up if it wasn't required? When it did work in the cold spell adjusting the temp required did result in the unit modulating the temperature quite well.

Scrump said:

I have the same vintage truma unit in my van. Mine is temperamental after I have turned the gas off, after opening tne gas supply it will start but then cuts out. Eventually it will run, but if I leave the gas turned on then it runs perfectly every time.
No idea about the electrical issue, mine is connected to a power management system with two leisure batteries and the van battery connected via smart controller.

I thought it could be gas delivery but a change of regulator, different bottles and running other gas appliances at the same time/trying different combos seemed to always result in the same outcome. It was purely a disconnected battery that would enable it to fire up. It's a confusing one.

donaircooleone said:

Truma C series?

As you've isolated the appliance and supplied another power supply I'd still be inclined to test the original wiring and check for other negative influences. Some appliances can be really funny with voltages especially if you have some misbehaving chargers (not always obvious with a multi-meter).

Yes a C4002 or something like that from memory. I did think maybe the charger was causing weird voltage fluctuations or that if the unit saw over 14v would assume the vehicle is on the move and automatically shuts off? I cannot find any info on if the unit does this. I removed the charger from the boats electrics (even the solar charger) and still didnt fire up

Caddyshack said:

Is it voltage sensitive? Maybe test the actual voltage you are seeing on the boat - I know you typed that it doesn’t drop but you didn’t say the actual voltage.

I had an issue in our camper, it was in the high 11 volts which some things did not like, I adjusted the solar controller to 13v and everything was then very happy.

This is my theory, but using a meter I see voltage between 12.5 and 13.5v depending on state of charge which seems fine. I've had the meter on the heater terminals and the battery terminals and with the thicker gauge wire see no voltage drop when it attempts to fire up. I even tried different batteries that had varied levels of charge and they all worked. As long as they were isolated from the boat electrics.

Since I bought it I always thought the battery wiring/chaging setup is a bit of a mess and requires a complete rethink. So think I will get that all straight, see if there is any weirdness that all the years of tinkering has introduced and try again from there. Any other options? Because I'm struggling especially in light that it did work fine on the unaltered electrics 6 months ago.

[Caddyshack]

Victron do some nice controllers and they have a potentiometer on the back so you can adjust the voltage to the desired amount and they will keep it at that.