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

[Pablo79]

Hi all. A month ago I was away in my van for a week on my own, and I didn’t run out of hot water. Now, every time I shower, I run out.

 

The Truma 6e should hold 10l of hot water. The water gets to temperature... it’s super hot. The indicator on the control panel stops flashing, tell me the water is hot, but when I turn on the tap I get 3-4 litres. That water is very hot... there’s just not enough and far below spec. I tested it by measuring how much hot water came out of the tap.

 

I contacted truma support and they weren’t too helpful. They said to make sure I used Gas or Mix, and to give it time. These things make no difference... the water is hot, but only a few litres.

 

Any ideas? Blockage? Air gap? I’m away in the van at the moment

 

 

[tonyishuk]

There is some on another forum. https://www.motorhomefun.co.uk/forum/threads/truma-combi-e-with-cp-plus-control-not-enough-hot-water.208181/

 

With some further links at the bottom of the page.

 

Some information on this site search, but the impression I get is that generous shower times are limited.

 

Rgds

[Pablo79]

Thanks for that.

 

It’s definitely a weird one. I measured the hot water coming out with a measuring jug and got somewhere between 3-4 litres, far below the 10l that should be provided. The water is very hot on gas, elec and mix, so it’s not a heating issue. More of a capacity issue.

[Derek Uzzell]

Pablo79 - 2021-06-03 7:12 AM

 

...The water is very hot on gas, elec and mix, so it’s not a heating issue. More of a capacity issue.

 

Every Truma “Combi” has a water boiler with a 10-litre capacity.

 

Using gas to heat the water will eventually raise the water temperature to a maximum of 60°C when the heating operation will shut down.

 

If that hot water is then used for showering the hot water will start being delivered towards the shower-head through an outlet near the top of the Combi’s water boiler and cold water will begin to enter the boiler through an inlet near the Combi’s base. Shortly after that cold-to-hot water transfer process starts, water heating will recommence.

 

Showering can use a lot of water and, if a showerer treats a Combi like a household domestic water heater that can provide copious quantities of hot water, the 10 litres of hot water in the Combi will rapidly be diluted temperature-wise by the cold water being pumped into the boileri via its low-level inlet. This is perfectly normal, but can be an unpleasant surprise to the innocent showerer unfamiliar with how a Combi functions.

 

My first two motorhomes had Trumatic C-series heaters with a 12-litre water capacity and showering was normally straightforward. My current Rapido has a gas-only Combi 4 and showering requires extra care as a result of the 2 litres reduction in capacity.

 

Nowadays I bring the boiler’s water temperature up 60°C and my wife takes her usual lavish shower. When she’s finished I ask her “Is that water still hot?” and if there’s any doubt I delay my own shower until the water’s temperature has returned to 60°C. I’ve learnt the hard way that, if there’s insufficent hot water in the Combi to offset the cold water that’s entering the boiler as the hot water is being drawn off, cold water will suddenly begin to spray from the shower-head and, if one is lathered in soap when that happens, the experience ain’t much fun unless one has serious masochistic proclivities.

 

(What I also found was that the “Ecocamel” shower-head that was part of the Rapido’s standard specification was (despite its water-saving marketing) unsuitable for how my wife and I shower and I've replaced it with a simple stick-type shower-head that’s less ‘thirsty’.)

 

So it is a “capacity issue” in that a Combi boiler only holds 10 litres of water, but - when it comes to showering comfortably and cursing-free - it’s primarily a ‘procedural’ issue.

[Pablo79]

Thanks for the reply. I know it's a different experience to showering at home. I never used to run out of hot water when showering though.

 

If we forget the shower for a moment, I actually measured with a measuring jug the output of hot water from the tap. Full hot, no cold water added, and water well up to temp. The water came out very hot for about 3.5l, and then it starting coming out cold. It's like the tank capacity is reduced. I get less than half of the 10l specification.

 

Really confused by this one. I wonder if I need to take it somewhere for an inspection or service.

[laimeduck]

As a sailor - I've spent many 2 week holidays bareboating in the Med and also cruising the UK, you get used to a showering procedure to absolutely minimise water use. If you are offshore, there are no supply taps! Even though you're floating on the stuff it's unusable.

Get in shower, Wet hair and upper parts. Turn water off ASAP.

Lather up all over.

Rinse briefly, from the top, turn off water, then use flannel to remove lathery water.

Job done with about 1-2 litres water.

 

Or...... simply "mature", and have a swim in a bay before entering port somewhere!

[Pablo79]

I probably shouldn't have mentioned the word shower (lol)

 

This is a hot water capacity issue. Thanks for the reply though!

[BruceM]

I think that what’s significant here is that the op has pointed out that this is a recent development, ie he did not previously run out of hot water.

 

A question; when you state that the water goes cold after 3.5lt of hot do you literally mean cold or is it just not quite so hot, and is there any change in flow rate?

 

I think I’d also be interested to know if the same issue arises if the hot water capacity is measured from a tap instead of the shower just to rule out something strange going on with the shower tap cartridge.

[Pablo79]

BruceM - 2021-06-03 9:36 AM

 

I think that what’s significant here is that the op has pointed out that this is a recent development, ie he did not previously run out of hot water.

 

A question; when you state that the water goes cold after 3.5lt of hot do you literally mean cold or is it just not quite so hot, and is there any change in flow rate?

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

 

The water temp drops off rapidly. I'd estimate that within half a litre, it's goes from full hot to full cold. It doesn't feel that the hot water is being diluted. It's a pretty sudden drop off.

[Pablo79]

And no noticeable change in flow rate. I wasn't looking out for this though, so I'd need to test it again to confirm.

[Derek Uzzell]

Pablo79 - 2021-06-03 8:45 AM

 

...The water came out very hot for about 3.5l, and then it starting coming out cold. It's like the tank capacity is reduced. I get less than half of the 10l specification...

What you’ve described is exactly what I’d expect to occur.

 

Through the tap you are taking 3.5litres of hot water from the Combi’s boiler and, as you do this, your motorhome’s water-pump will be pumping cold water into the bottom of the Combi’s boiler where it will mix with the hot water and reduce that water’s temperature. This mixing process is unavoidable.

 

You’ve said "The water came out very hot for about 3.5l, and then it starting coming out cold...” This is the effect of the mixing process and, if you continued to draw water from the tap you’d soon get completely cold water coming out. The shift from hot to cold can be surprisingly rapid.

 

You seem to believe that, after your Combi has produced 10 litres of water at 60°C in its boiler, you will be able to draw off the full 10 litres of 60°C water without the temperature of that water reducing. But that’s not possible as, whatever you do, cold water is going to enter the Combi’s boiler and cause the temperature of the water in it to drop.

 

There’s absolutely nothing ‘wrong’ with your Combi, you just need to appreciate that this is what Combis do and adapt how you use the appliance accordingly.

[Pablo79]

Derek Uzzell - 2021-06-03 9:50 AM

 

Pablo79 - 2021-06-03 8:45 AM

 

...The water came out very hot for about 3.5l, and then it starting coming out cold. It's like the tank capacity is reduced. I get less than half of the 10l specification...

What you’ve described is exactly what I’d expect to occur.

 

Through the tap you are taking 3.5litres of hot water from the Combi’s boiler and, as you do this, your motorhome’s water-pump will be pumping cold water into the bottom of the Combi’s boiler where it will mix with the hot water and reduce that water’s temperature. This mixing process is unavoidable.

 

You’ve said "The water came out very hot for about 3.5l, and then it starting coming out cold...” This is the effect of the mixing process and, if you continued to draw water from the tap you’d soon get completely cold water coming out. The shift from hot to cold can be surprisingly rapid.

 

You seem to believe that, after your Combi has produced 10 litres of water at 60°C in its boiler, you will be able to draw off the full 10 litres of 60°C water without the temperature of that water reducing. But that’s not possible as, whatever you do, cold water is going to enter the Combi’s boiler and cause the temperature of the water in it to drop.

 

There’s absolutely nothing ‘wrong’ with your Combi, you just need to appreciate that this is what Combis do and adapt how you use the appliance accordingly.

That's very interesting.

 

So why would it suddenly be different to how it was a few weeks ago? Previously two of us could shower consecutively, if conservative, without any loss of hot water. Now, with the same conservative approach, one of us can barely finish without it going cold before the end.

 

Had the boiler always behaved this way, I wouldn't be concerned and would accept it, but that's not the case.

[BruceM]

BruceM - 2021-06-03 9:36 AM

I think I’d also be interested to know if the same issue arises if the hot water capacity is measured from a tap instead of the shower just to rule out something strange going on with the shower tap cartridge.

As some of our posts crossed (because I edited) you may have missed my diagnostic suggestion above

[Pablo79]

BruceM - 2021-06-03 10:05 AM

 

BruceM - 2021-06-03 9:36 AM

I think I’d also be interested to know if the same issue arises if the hot water capacity is measured from a tap instead of the shower just to rule out something strange going on with the shower tap cartridge.

As some of our posts crossed (because I edited) you may have missed my diagnostic suggestion above

I did miss that, thanks Bruce. 'll give that a try when I'm back at the van this evening.

[Derek Uzzell]

I can't provide an explanation as to why your Combi has changed its behaviour other than to suggest that it is no longer heating to the full 60°C and the cold-water 'mixing' is having more effect.

 

There's a cross-section drawing of a Combi 6E here

 

https://www.truma.com/uk/en/company/truma-press-overview/truma-combi-6-e-with-new-features-

 

Although it's not apparent from the drawing, the cold-water inlet and hot-water outlet are both offset towards one side of the heater (ie. towards the far side of the Combi in the drawing) and the result is that, when cold water enters the water boiler it has a rapid impact on the temperature of the water being drawn out.

 

I suppose there is the possibility that your Combi is very heavily 'limescaled' inside (as happens with kettles in hard water areas) and that has radically reduced the boilers capacity. But that wouldn't explain the sudden change in behaviour. This 2008 forum thread related to Trumatic C heaters, but the descaling procedure would be similar.

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Hints-and-Tips/Descaling-Truma-water-heater/13476/

[onecal]

Hi

Looks like your boiler may not actually be heating up to 60oC and also may be coated internally with lime scale ( As Derek has pointed out to you)

This will not allow hot water for too long at the taps or shower ,

Take a temperature reading your hot water see does it actually get to 60oC at all (or overheating and cutting out)

Regards

[Pablo79]

Thanks for that everyone.

 

It's definitely up to temp! It's super hot, and no cooler than usual.

[tonyishuk]

Some odd thoughts !

 

Does the amount of hot water vary depending on the supply of heater.

 

Ie. Electric or gas or electric AND gas

.

Are there separate sensors depending for gas or electric being used ? I guess there would only be one, but who knows.

 

Could the sensor have slipped or moved if fitted on a belt on the cylinder, rather than a permanent fixed position.

 

Rgds

[flicka]

Can you check at what point the boiler is reigniting ?

If the temperature sensor is beginning to fail at high temperature it would delay reigniting the boiler.

I find reducing the flow rate after initial wetting gives the boiler a chance to"catch up" & give a longer shower at a lower but reasonable temperature.

[Derek Uzzell]

tonyishuk - 2021-06-03 10:32 PM

 

Some odd thoughts !

 

Does the amount of hot water vary depending on the supply of heater.

 

Ie. Electric or gas or electric AND gas

.

Are there separate sensors depending for gas or electric being used ? I guess there would only be one, but who knows.

 

Could the sensor have slipped or moved if fitted on a belt on the cylinder, rather than a permanent fixed position.

 

Rgds

This .pdf file relates to the Truma Combi 6E (UK) heater and includes an exploded-view drawing and a spare parts listing.

 

https://www.leisurespares.co.uk/files/ww/combi%206%20e%20uk.pdf

 

In your last sentence you may be thinking of the ‘belt’ arrangement that provided an optional 230V water-heating capability for Trumatic C heaters (other than the C6002EH model), but Combis don’t use that system.

 

My understanding was that - where a Combi 6E’s water heating is concerned - there is a single thermostat mounted on the outer surface of the water container’s casing, and the details on the .pdf file seem to confirm that this is indeed the case. This thermostat measures the temperature of the water container’s casing (and, hence, the temperature of the water inside the container) and the water temperature limit (40°C or 60°C) is controlled electronically. Whichever ‘fuel source’ has been selected (gas, 230V or both together) should not alter the 40°C/60°C limits.

 

Delivery of water from a Combi will depend on the capability of a motorhome’s water-pump. The higher a pump’s flow-rate and the higher the pressure it can exert, the greater the volume of hot water that can be drawn from the boiler in a given period of time, but - in practice - as long as the pump’s performance is adequate, this won’t really matter.

[Derek Uzzell]

flicka - 2021-06-03 11:36 PM

 

Can you check at what point the boiler is reigniting ?

If the temperature sensor is beginning to fail at high temperature it would delay reigniting the boiler.

I find reducing the flow rate after initial wetting gives the boiler a chance to "catch up" & give a longer shower at a lower but reasonable temperature.

Pablo’s problem does not relate to water ‘reheating’, nor specifically to showering.

 

He runs the Combi until its control panel indicates that the temperature of the water in the 10-litres boiler has reached the desired temperature (presumably 60°C) but - when he then draws hot water from a tap - he only gets about 3.5litres of piping hot water before the water coming from the tap goes cold.

 

Where this ‘only 3.5litres of hot water’ issue really does impact, of course, is when Pablo’s Combi is used for showering and he has emphasised that two people used to be able to shower consecutively (if conservatively) using a single tankful of hot water, but that’s no longer possible.

 

”...Previously two of us could shower consecutively, if conservative, without any loss of hot water. Now, with the same conservative approach, one of us can barely finish without it going cold before the end.

 

Had the boiler always behaved this way, I wouldn't be concerned and would accept it, but that's not the case.”

 

If, when Pablo experiments by drawing off water from a tap, that water proves to be at the expected temperature, the only possibility remaining seems to be that his Combi’s water container is holding much less than 10 litres, and the only way that could happen is if the container is massively ‘limescaled’ inside. (Can’t say I care for that idea much though...)

[Brian Kirby]

There are several theoretically possible explanations. I assume that for safety reasons there must be a high-limit stat of some sort to shut down the heater if the service thermostat fails. Just thinking of the references to "super-hot" water, I wonder if this might be the case?

 

Alternatively, the "thermostat" (or its electronic control function) may have become defective, and be shutting down the heater before all the water has been heated. It might be interesting to repeat the tests at 40C to see if the full quantity is then delivered.

 

As this seems to relate primarily to showering, is it possible a water connection has loosened, allowing a proportion of the water intended for the shower head to run away elsewhere? But, one would imagine this would have become apparent!

 

Might it be possible, as suggested above, for the thermostat to have slipped into a position from which it turns off heating before the full capacity is heated?

 

Either something is turning off the heating before the full capacity has been heated, or the capacity of the heater is somehow reduced by 50% - which seems improbable in so short a period of time - or half the hot water is escaping en-route to the shower/taps.

[weldted]

Just for some info? Powered up our our combi earlier today, when up to temp will produce around 5.5 litres at around 55c then starts to drop off to below 50c by the time you get 9 litres it’s less than 30 at 10 litres Luke warm hope that helps.

[tonyishuk]

Thank you for the PDF breakdown of the Heater, technology has moved on from our trusted installation!

 

I suppose at the end of the day ; it’s not so much “ how long can I have a hot shower” more “how much can I warm the cold water to be bearable”. Something I have discovered since being banned from the CMHC toilet blocks by the Navigator in case I bring back something catching ;-)

 

Rgds

[Derek Uzzell]

Brian Kirby - 2021-06-04 6:52 PM

 

There are several theoretically possible explanations....

Pablo said in his original posting

 

The Truma 6e should hold 10l of hot water. The water gets to temperature... it’s super hot. The indicator on the control panel stops flashing, tell me the water is hot, but when I turn on the tap I get 3-4 litres. That water is very hot... there’s just not enough and far below spec. I tested it by measuring how much hot water came out of the tap.

 

As Pablo subsequently emphasised, ‘showering’ is a red herring and his 3-4 litres of hot water came from a tap. It was suggested above that it would be worth Pablo confirming what the temperature of the “super hot’ water actually is, but 60°C is definitely "super hot" and 40°C is definitely not.

 

There’s no indication of a physical secondary thermostat on the Combi 6E drawing, but there will be some means to prevent the Combi heater continuing to heat water until it boils, and the appliance will go into fail mode if Summer operation is chosen and there’s no water in the boiler. But this is academic in Pablo’s case as - when he has selected water heating via his CP Plus control panel - the heater behaves exactly as one would expect, with the panel flashing while water heating takes place and ceasing flashing when (presumably) the chosen water temperature has been attained.

 

There’s no way for the thermostat on the water container’s casing to ’slip’ and the Combi to still function as Pablo has described. If (somehow) the thermostat became dislodged, it would be unrealistic to believe that the appliance would behave as it does during the water heating process.

 

Weldted’s Burstner is 2 years younger than Pablo’s Benimar, so - if build-up of limescale inside Pablo’s Combi were the problem - that MIGHT account for Weldted’s greater volume of hot water being produced from a single heating phase.

 

There is (as you’ve said) the possibility of a significant hot water leakage that would allow cold water to enter the boiler while water was being heated, but I would have thought that this would impact on the heating phase itself (ie. the heating phase would last longer) - besides which, if hot water were leaking out, the motorhome’s water pump would be pumping cold water into the heater to keep up with the water loss and Pablo would almost certainly notice the pump running when all the water outlets were closed.

 

(Truma’s FrostControl safety/drain valve is designed to ‘vent’ if the pressure in the water system during the water heating phase gets too high (my Rapido’s FrostControl valve does this) but the venting is only momentary and just a tiny amount of (cold) water is spat out through the valve.)

 

Dunno - but if limescale is the culprit, the only way to cure the problem will be to descale Pablo’s Combi.