Truma Ultrastore Water Heater

[gearykyle]

When i first bleed the air out of the hot water tap and switch on the power i get a hot water. After using the hot water for showering etc it starts to run cold suggesting the the thermostat is not working to allow power to return to reheat the water. If i then turn the power off and leave for 5 mins and then turn on again the water will heat up.This happens repeatably. Any suggestions to remedy this problem.

Hi Baz - from NZ - I know this post was a few years ago but I am having same issues with my Truma Waterheater - heats up great from filling it, then I use some water and it goes cold but can only get it hot again by turning the unit on and off.
Element and Thermostat are fine - all tested great. Did you get yours sorted in the end or did you simply replace the element?

 

[IanB1485]

The older heater elements were 450W and later ones 800W also we can get 1200W heater elements (non Truma) The 450W versions weren't the fastest to reheat. How long do you leave it? or have you tried waiting with it on? The simple thermostat is bolted quite close to the heater element and probably has quite a large hysteresis, so will have to cool down quite a lot before switching back on on its own , Removing the power doesn't reset it , a reduction in temperature as its just a simple bimetallic switch. if it is failing ( hysteresis getting bigger) then replacement of the heater element ( the 800W and 1300W come with the thermostat wired in. The 450W had a separate thermostatic switch. You need to open up the outer cardboard cover where the mains wires go into the unit to see which version you have.I have never seen a 450W version , but I believe the 450W heater unit is not physically compatible with the 800W replacement heater assemblies.

 

[gearykyle]

Thx Ian
Its an 800w version. BN-103 Model. I have left it on for a long period hoping it would reheat but the only way to get it back to hot is to turn the main switch off, wait for 5 mins, turn back on again and wait for it to reheat - same issue Baz had. My feel is that it should keep the same heat continuously as we only use it for dishes (no shower or bathroom in the van) ie, there is no way we are using 10L every time we do dishes.
I have tested the existing Element and Thermostat and get good ohm readings - plus the heater does heat up initially so it cannot be an element issue.
Possibly air getting in somewhere but then I have re-inserted all the John Lewis fittings, even replaced a few, and re-tightened all the plastic screw/bolt fittings.

 

[Martin_E]

Have you tested the thermostat when the heater has heated the stopped?
It could be that the heater is getting to hot on heating up and tripping the thermostat, or tripping to early, the kind of give away is that it resets when the mains is interrupted, then off it goes again.

 

[gearykyle]

Have you tested the thermostat when the heater has heated the stopped?
It could be that the heater is getting to hot on heating up and tripping the thermostat, or tripping to early, the kind of give away is that it resets when the mains is interrupted, then off it goes again.

Thanks Martin,
I will try that when back from a current work trip. Though what would cause the heater to get too hot do you think,?

 

[Martin_E]

It could possibly just be the thermostat isn’t resetting as well I guess

 

[Dustydog]

This video may help

View: https://www.youtube.com/watch?v=CsCvUHPb-wE


Note not all have two levels of heating but the principle is the same.

 

[IanB1485]

The thermostat is a simple bi-metallic switch end of . One test would be to remove and touch a hot soldering iron against active surface of the switch and measure the combined resistance ( no power on obviously) when it goes to infinity( >10M ohms ) remove the soldering iron and if possible place a thermometer ( digital with a type k thermistor or 100 Ohm Platinum resistance probe) against the active surface and note at what temperature it resets . The only simple device I know of which will reset once power is removed is a polyfuse ( basically a positive temperature coefficient thermistor ). but those are only used to protect electronic circuits from overload if incorrectly connected. The thermostat relies heavily on the mechanical construction of the switch hinge being intact and any damage/degradation may alter its characteristics . IMO replacement of the heater element assembly is the only solution, by time you have dragged the old one out and checked it , you might as well replace the assembly.If you are no good at assembling flat pack furniture you may want to call an engineer , Reassembling the cardboard cover is an artform in itself Here's a couple of ones which failed with earth leakage , you can see the bimetallic switch is potted as are the connections of the heater connections.If you buy a heater element off Ebay , be careful that the gasket supplied does seal the heater to the tank.

 

[Martin_E]

@IanB1485 I am not sure why you need to remove the cardboard, Truma put a pre punched cut out to allow access to the element . The element change can be done nice a neatly using the cut out…….unless someone just rips the ears of the stamped cut out open by hand rather than a sharp knife.