Truma 6e - water is hot, but not much of it!

[Brian Kirby]

I agree. But Pablo also said "Exactly right. My last week in the van was a month ago, and I didn't have any hot water capacity issues."

 

So he appears to be describing a very noticeable change in the way the heater is operating over a period of one month, during which time it seems it was unused. If the change is, indeed, due to limescale build-up it would surely require a huge deposit to reduce the heater capacity by so large an amount? I suppose such a build up could occur if the hot water side were not regularly drained, but even so!!

 

I suspect the water temperature control is in fact via a thermistor (and not a 'stat), which emits a signal (in the form of variable voltage) back to the CP Plus to interpret. That raises the further possibility (which has only just occurred to me) that the fault might be in the CP Plus, or that some unintended change to its heating control range may be the cause.

 

BTW, the leakage I had in mind was in the hot water distribution pipework downstream from the boiler, causing some hot to leak to waste whenever hot was was demanded, and so simply run out prematurely. However, that would result in relatively large amounts of water being dumped inside the van, which Pablo would surely have noticed? I assume Benimar don't run any h/w pipework under the van. They wouldn't, would they? Well, you never know! :-)

[laimeduck]

Brian Kirby - 2021-06-05 11:53 AM

 

I agree. But Pablo also said "Exactly right. My last week in the van was a month ago, and I didn't have any hot water capacity issues."

 

So he appears to be describing a very noticeable change in the way the heater is operating over a period of one month, during which time it seems it was unused. If the change is, indeed, due to limescale build-up it would surely require a huge deposit to reduce the heater capacity by so large an amount? I suppose such a build up could occur if the hot water side were not regularly drained, but even so!!

 

I suspect the water temperature control is in fact via a thermistor (and not a 'stat), which emits a signal (in the form of variable voltage) back to the CP Plus to interpret. That raises the further possibility (which has only just occurred to me) that the fault might be in the CP Plus, or that some unintended change to its heating control range may be the cause.

 

BTW, the leakage I had in mind was in the hot water distribution pipework downstream from the boiler, causing some hot to leak to waste whenever hot was was demanded, and so simply run out prematurely. However, that would result in relatively large amounts of water being dumped inside the van, which Pablo would surely have noticed? I assume Benimar don't run any h/w pipework under the van. They wouldn't, would they? Well, you never know! :-)

My Benimar's water pipes are all run inside the van, though it is somewhat older than Pablo's. Bizarrely the hot air ducting to near the cab does run underneath, albeit heavily insulated.

 

I do not buy the build up of scale theory. That would imply that the system had furred up to the tune of about 5 litres over 30 days! Not possible surely?

 

Pablo, have you tried draining the system, then refilling? If there were an air pocket trapped somewhere that might clear it?

(Rather like re-starting a computer that is playing up?)

 

Jeremy

[Derek Uzzell]

I'm not comfortable with any of the hypotheses put forward so far - including my own.

 

Jeremy's 'air pocket' suggestion might explain the symptoms if the Combi's water container were part empty (ie. there's (say) 7 litres of water in the container's lower section and the upper section contained 3 litres of air) but I'm not sure if that scenario is possible and, in any case, the issue evidently repeats.

 

I agree with Jeremy (because I can't think of any credible alternative). Start from scratch, drain down the system, refill and very carefully bleed it until all the water outlets run with no sign of air emerging - then fire up the Combi in water heating mode and see what happens.

[Derek Uzzell]

An aftertought...

 

Although it would be very odd for the capacity of the water boiler of Pablo’s Combi to have somehow reduced about a month ago, it should be possible to confirm whether, when the boiler has been filled, it holds 10 litres.

 

Fill the Combi’s tank, then put a bucket beneath the motorhome where the pipe from the (FrostControl?) drain valve emerges and open the drain valve, then - after draining ceases - measure how much water is in the bucket.

 

Obviously care would need to be taken to ensure that the water that goes into the bucket comes only from the Combi, but I could carry out this procedure with my Rapido so that the amount of water imeasured in the bucket would confirm (or otherwise) that the boiler was holding 10 litres.

[Brian Kirby]

Derek Uzzell - 2021-06-05 4:15 PM......................Start from scratch, drain down the system, refill and very carefully bleed it until all the water outlets run with no sign of air emerging - then fire up the Combi in water heating mode and see what happens.

Having done that, open all the hot taps again until there is no spitting or spluttering, as I've always found that a small amount of air emerges once up to full temp however thoroughly I think I've bled it before the water heating had been run.