Truma water heater

[Tomsdad]

Hi everyone. 2nd post about the Birchwood 25 recently purchased. It has a Truma 10 litre water heater. Heats from gas or 230volt shore power. Was testing it yesterday from mains power. All went well supplying hot water to kitchen and bathroom. Until after about 30 mins there was a loud bang.
Hot water spaying everywhere. On inspection there is a clear 10mm tube teed on the red ( hot) output. And previous owner had blocked tube with a drill bit and jubilee clip. So it was a deliberate act. The bang was the tube being blown off the output.
My theory is that the Truma developed a fault which continuously tipped water out the tube. But instead of fixing the fault he just blanked off the pipe and didn’t use the water heater. This still allowed cold water feed to the taps.
Anyway I need to sort the problem. I took the output tee connection off to inspect. I thought there would be a broken one way valve. Couldn’t see any valve and could blow through in both directions.
Any help much appreciated.

 

[wallacebob]

Truma are very common in caravans; might get more response at CMHC Forum. Used to a very helpful engineer posted there.

 

[ProDave]

We have the identical heater in our caravan. Known by caravanners as Traumatic heaters.

Your issue is pressure build up as the water heats up. How is your hot water supplied? Pressurised system with a pressure sensor that operates the pump, or (more common on caravans) a microswitch on the taps to turn the pump on.

Either way it needs to expand somewhere as the water heats up. I see no expansion vessel on ours so I suspect it expands by pushing cold water back out of the inlet back to the tank? Or is is like the Megaflow domestic hot water cylinders that just have a bubble of air in a domed top (the Truma has a domed top if you take the lid off for a look)

These heaters are tiny, only 10L of water. It should have heated and shut off in way less than 30 minutes, so my first place to look would the the thermostat, I would not be surprised if you have a failed thermostat and it was on the verge of boiling at which point the pressure build up would be immense and your bodged dead leg of pipe was the weakest link. Be thankful you did have that accidental safety valve. I suspect your "drill in a pipe" is nothing more than a way to close off a pipe that is no longer used.

A previous one on a previous caravan had a leak I had to fix twice, it is a stainless steel tank with stainless steel inlet and outlet pipes but they are not welded in, rather soft soldered with stainless steel solder.

 

[Tomsdad]

thanks for that. The taps don’t operate the pump. Pump comes on and off irregularly so would be pressure operated.
One other thing tho. If I now fill the main boats water tank the Truma fills up automatically and will push water out of the clear tube as soon as the water level reaches the output tee. This happens without the Trauma even being switched on.
I had thought that clear pipe would have had a one way valve to let air in but not water out?
But the thermostat. Is that accessible or is it part of the heating element? But as this is now happening from cold I can’t see the link to the thermostat.
Do you know why the clear tube is there. What its function is?
Appreciate the help

 

[ProDave]

Your dead end pipe is a red herring. It needs to be plugged or water will just run out. but it serves no purpose. It should never need to let air in. Best thing in the long term is remove it by replacing the tee on the outlet from the heater with an elbow.

With the end plugged again turn the heater back on and keep an eye on the temperature and how long the heater stays on. If the heater does not turn off after 15 minutes I suspect you have a problem, then run some water and see how hot it is.

 

[DinghyMan]

I think you will find that the clear pipe is the overpressure relief outlet on the outlet pipe - if pressure to the water heater exceeds 2.8bar water will be released out of the clear pipe, these often weep as they come up to temp and should not let water through when you fill the heater with water

It should not be blocked

Sounds like outlet valve overpressure section needs replacing

 

[DinghyMan]

Your dead end pipe is a red herring. It needs to be plugged or water will just run out. but it serves no purpose. It should never need to let air in. Best thing in the long term is remove it by replacing the tee on the outlet from the heater with an elbow.

With the end plugged again turn the heater back on and keep an eye on the temperature and how long the heater stays on. If the heater does not turn off after 15 minutes I suspect you have a problem, then run some water and see how hot it is.

It does serve a purpose and is there as part of the fitting process, and is shown in the manuals

It should never be plugged

 

[ProDave]

It does serve a purpose and is there as part of the fitting process, and is shown in the manuals

It should never be plugged

Thanks. So in this case the fault is in the OP's case, the pressure relief valve is missing and has been wrongly replaced with a drill bit and jubilee clip to plug the end of the pipe.

I still think there is another fault for it to get up to 2.8 bar. Like the thermostat failed and it was near boiling which should still be checked after replacing this pressure relief valve with the correct part. Certainly the one in my caravan does not have this valve and at no time does it build up that much pressure in the pipes. A pressure relief valve is to prevent a bigger bang if the whole tank bursts, it's discharging should not be normal.

 

[DinghyMan]

Thanks. So in this case the fault is in the OP's case, the pressure relief valve is missing and has been wrongly replaced with a drill bit and jubilee clip to plug the end of the pipe.

I still think there is another fault for it to get up to 2.8 bar. Like the thermostat failed and it was near boiling which should still be checked after replacing this pressure relief valve with the correct part. Certainly the one in my caravan does not have this valve and at no time does it build up that much pressure in the pipes. A pressure relief valve is to prevent a bigger bang if the whole tank bursts, it's discharging should not be normal.

Agreed - from the OP's description it sounds like the internals from the valve are missing

The valve comes as part of the fitting kit and should be on the outlet, Truma call it a "Water Heater Safety Drain Valve" on some models

The one in your caravan should have one fitted somewhere and the type and fitting position vary widely between models, often they are just a pressure relief valve not a combined outlet T / drain / pressure relief all in one

 

[ProDave]

Looking at the one in my caravan, it has a similar valve but through the floor, and that doubles as a manual drain valve. obviously through the floor would not work on a boat so they have an alternative relief valve.

 

[Tomsdad]

Quick update
Spoke with Truma customer services this morning. They were very clear that there IS a valve in the red output tee.
They asked for a photo so they can identify the correct replacement. Apparently there are 4 different types.
As soon as I have purchased/ fitted the replacement we can see what works and what doesn’t and take it from there.
Appreciate all your help.

 

[Tomsdad]

So an update. Apologies for delay. Been down to the boat and replaced the red “hot” output tee with a new one which has a one way valve in it. Now I fill the main water tank on the boat. This automatically fills the Truma. Switch mains on. Water heats up. No leaks and no water coming out the clear tube. But after 30 minutes the water is a bit too hot. You wouldn’t keep your hand under it. But apart from that no problems. Now I still think there may be a problem with the water getting too hot. From what I can research, when used with mains power the temperature is pre set. Not adjustable. But I don’t think it would be preset to how hot it is now. So the heating element obviously works and there is presumably a preset built in thermostat?
I need the courage to leave it on for an hour or so to see what happens.
Any suggestions welcomed.