I was recently called out to a customer that could not get his caravan room heater to stay lit on gas. When the gas selector knob was pressed in, the gas ignited and would burn clean and strong but would extinguish as soon as the gas knob was released. I immediately suspected the thermocouple to be at fault which is normally a simple job to replace, or so I thought before looking under the van.
23 years of exposure to the elements, not to mention road spray and salt had taken its toll, not only on the braided outer cover of the thermocouple but the main burner casing as well. Strip down was going to be the first issue followed by the availability of spare parts for a heater that has been out of production for many years. After making several enquiries with trade suppliers and Carver specialists, I was told that the parts I required were no longer available for this heater so some lateral thinking was required. I know that Truma took over the Carver brand in the past and carried on production of Carver heaters alongside their own, very similar Truma room heaters so I took a gamble and ordered a Truma thermocouple even though there was no guarantee it would fit or work.
After removing the heater from the caravan, it was placed upside down on a work bench to start the strip down of what now looked like a rusticle from the Titanic. The bolts holding the cover plate in place had to be drilled out and after some careful prising of corroded sheet metal I was able to expose the burner and thermocouple locknut.
The burner was in good condition and the thermocouple locknut was easily undone but unfortunately the same couldn't be said for the other end where the thermocouple screwed into the base of the gas valve. Several factors came together to make removal by simply unbolting the thermocouple an impossible task. Rust, corrosion and dissimilar metals meant that the moment I started to undo the brass thermocouple bolt it sheared off in the aluminium housing.
I tried to remove the aluminium housing with a 19mm spanner but it wasn't going to budge no matter how much I swung on it and without removing it, it was game over. As with every other step so far it was a case of trying something that had two possible outcomes, one successful and the other a total write off of the heater. So far so good but without unscrewing the aluminium housing I wouldn't be able to drill out the remains of the thermocouple and re-tap a new thread. I couldn't get it undone no matter what I tried but just before giving in and admitting defeat I decided to get out the big guns. Literally, A 380Nm impact gun. Now this was either going to remove the nut or destroy the gas valve it had become welded to. I didn't hold out much hope and warned the customer of this do or die last ditch attempt but to my surprise and great relief it actually worked.
I carefully drilled out the old thermocouple but then came the next stumbling block, what size tap do I need to recut a thread for the new thermocouple. Searching the internet came up with no results, neither did consulting with fellow caravan engineers, so again I had hit another brick wall and progress was halted. Eventually, more by luck than judgement I was able to speak to someone that used to work with Carver room and water heaters, he informed me that he thought the thread was M8 fine but couldn't be certain. Well yet again it was a case of trying something that may work or render the heater totally useless. I decided to try tapping an M8 fine thread as I had nothing to lose and it worked.
The final stage of this engineering project was reassembly and test which I am please to say was a resounding success as the heater now lights on gas, stays lit as it should and works perfectly.
So why did I decide to give this blog the title A throw away society? If something doesn't work the normal reaction is to throw it away and buy new. My customer contacted several companies and engineers before reaching out to me and everyone told him his heater was obsolete, parts were no longer available, it couldn't be fixed and he would need to replace his heater with a new one.
Telling me it can't be done is like a red rag to a bull and I love a challenge. It's also very satisfying when you achieve a successful outcome at the fraction of the cost of total replacement and you leave a very happy customer.