Alde Convector & Hose Rebuild, Useful Truma/Alde part numbers, and a Modest System Improvement

I own one of the early Tab 400s, built in the summer of 2017, purchased in the fall. The 3010 Alde came with Century Transfer Fluid. I replaced it after 4 years, in 2021, then again 2 years later, in 2023, still using the Century Fluid. That year, I noticed some minor-looking bulging at hose connections near the Alde and thought I should do a thorough inspection of convectors when I did the winter 2025 fluid change. A month ahead of my scheduled maintenance, the corrosion build-up in the last stub connector in the return tubing before the expansion tank caused the hose to tear and leak all over the cabin floor during a 2-week, 2,000 mile trip. Dang.

From Truma Corp (now owners of Alde), I ordered 80 29 mm spring band clamps, 30 plastic stub connectors, and 3 meters of Alde EPDM 22 mm I.D. hose.

I cut 4 corroded ends off of convectors. Two were on the convector under the bathroom, nearest the stub where the tube tore and leaked, almost at the expansion tank return. I suspect that the transfer fluid farthest from the pump refreshed less over time and allowed more corrosion.

As part of the system rebuild, I covered all convector ends and the check-valve stub connector, which is aluminum, with adhesive-lined heat-shrink tubing. I also double-clamped almost all connections, 3 centimeters in, and at the tube ends. I reused all 90 degree rubber tube pieces, which were undamaged, but cut the ends off of all straight hose pieces, many of which had bulged with corroded aluminum oxide. By using a new piece of rubber tubing for the longest (2 meters, approx.) section, then using my slightly shortened pieces for every shorter section, sequentially, I only needed to buy 3 meters of hose.

Finally, I added two switched 3.5” computer fans just below the convector at the back of the trailer, behind the bed. This convector is the longest, but often partially blocked by bedding, and I thought it could use a boost.

This job was time-consuming, involving lots of awkward and cramped working positions. However, I think it was much more feasible DIY, and I was more successful, because of the multiple contributions and threads of others who have serviced and repaired their Alde systems.

What follows are notes on the rebuild process and components used, along with references to other threads which were the source of the methods used and choices made.





Alde started using plastic stub connectors instead of aluminum ones, probably around 2021, when they recommended switching from Century Transfer Fluid to Rhomar Water RG-RTU-50, aka Truma/Alde Transfer Fluid. This change eliminated a great deal of potential corrosion problems. pthomas745 provides a photo of these stubs in “Corrosion of Alde Connectors (see link above).” Unlike the aluminum connection fittings, they probably do not need to be double-clamped. However, I double-clamped almost every connection, from an abundance of caution. I prefer to over do it rather than have to ever deal with more leaks.


Alde EPDM 22mm I.D. Rubber Hose 35119-00002, sold by the meter, @ $4.37/M.
Connector Pipe 022 (AKA plastic stub connectors), 35119-00119, @ $1.55 per unit.
Band Spring Clip 29mm, 35119-00176, @ $1.03 per unit (and well worth it!). Shipping was quite reasonable for these items, in the quantities noted at the beginning of my post, under $20.

Alde Fluid. There are numerous threads on the forum on this, such as:

Several of these threads discuss the merit of using propylene glycol, with the correct anti-corrosion additives, and the danger of using ethylene glycol fluids. I purchased Truma Transfer Fluid from Amazon. Truma Corp. itself also sells it, at a higher price with steep shipping. NuCampRV sells Alde Fluid, but the shipping charges, at least for me, in Oregon, were $200/gal.! Rhomar Rhogard Ultra may be available from some Ferguson Supply outlets and other hydronic/plumbing supply sources, but normally it is only for commercial buyers, and, because it is concentrated, some of the 5 gallons (10 g when diluted for use) would have to last for up to six years. There is a discouraging lack of affordable options. But, given the time and money for repair, I think following the Truma/Alde recommendation is best. My system took about 2.6 gallons. After flushing the system with compressed air and reassembly, I filled it with distilled water and tested it. I used the hand pump method for filling, mentioned above in the referenced Glycol Exchange Guide. In addition to using the system pump on high speed, I use a drill pump to circulate the fluid at an even brisker speed, for a minute or so, to further purge out the air bubbles. I just fit female hose ends to the clear plastic tubing and stopper assemblies in the Guide. Then push the fluid down the intake hole in the tank while sucking it through the pump from the tank reservoir.



After testing, I again air-flushed out 2.6 gallons of water, then refilled with the same quantity of Truma Transfer Fluid.

While I had the convectors exposed I added these two 3.5” fans directly under the rear convector, wired them to a 12 V DC to 5 V DC USB converter, and from there to a switch. I spliced into the DC circuit for the Alde to do this.