Truma thermostat Sensor relocation (1 Viewer)

[Bart]

So I've finally got around to relocating the thermostat Sensor on our 6002 Truma heater in our Bessacarr E560 due the stupid location that it is mounted in ( above the habitation door at roof height ) which means that the heating does not cut in and out very well.
So atm i have just extended the wires on the sensor and am trying it out in different places when i noticed that it seemed to work well , as in keeping the MH a constant temp rather than before it being roasting and then having to turn down the thermostat , to discover 20 mins later the MH freezing with the heating not restarting again until you turned up the thermostat again by quite a bit.
Now i have tried the sensor about 6" from the ground on the side of the lounge seats and this seemed to work well , HOWEVER i did notice that the heater ran nearly constantly with the fan blowing at the SLOWEST speed it could , this seemed far better than previously where the Heater would NOT run for a long time but when it did run the fan ran at its FASTEST speed for most of the time until MH is like a sauna.
So yip i know i rambled on a bit but here is my QUESTION , will there be a difference in gas usage between
1. Heater running some of the time , but blowing the air out of it at its Fastest speed
2. Heater running most of the time , but blowing the air out of it at its Slowest speed

to me option 2 is far better , but i'm worried that the gas usage will rocket , as we only wild camp and the gas heater is used often.

Does the heater unit inside the heater burn gas at different speeds , the same way the 12v Fan in the heater blows at different speeds ??

 

[Boringfrog]

A bit like, do I boil the kettle with the gas turned up high or leave it low where it will take longer.....

With the cold weather as of late, the boiler fan running slow won't get the van up to temp so I will turn the thermostat right up, then down, then up again.

 

[tonyidle]

Can't answer the question but you are describing it running as intended. Once the thermostat reaches the set temperature it causes the heater to reduce the combustion fan speed. If the temperature in the van continues to rise the combustion fan will stop entirely and the heater is turned off. If the temperature continues to fall (after the initial turn-down to low speed) the heater will return to high speed. The intention is for the thermostat to be located where, once up to temperature, there will be no massive temperature swings and the heater will maintain a constant temperature without moving from low speed. So if you were in the past hearing the combustion fan regularly going onto high speed followed by adjustment or total switch off it simply means the thermostat was in the wrong place - but you knew that anyway.

Just to be clear: the fan affected by the thermostat is the combustion fan the speed of which determines the output of the boiler (ie the size of the flame). The fan that blows air through the tubes is a separate unit that simply notices that the heater is on and starts to blow. It's speed varies depending on how hot the boiler becomes but it has no effect on boiler output (or gas usage).

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[Bart]

So if you were in the past hearing the combustion fan regularly going onto high speed followed by adjustment or total switch off it simply means the thermostat was in the wrong place - but you knew that anyway.

Yip this is what was happening , and the heater does not come back on until the MH is freezing.

Just to be clear: the fan affected by the thermostat is the combustion fan the speed of which determines the output of the boiler (ie the size of the flame). The fan that blows air through the tubes is a separate unit that simply notices that the heater is on and starts to blow. It's speed varies depending on how hot the boiler becomes but it has no effect on boiler output (or gas usage).

Which fan is it that i hear when i first turn on the heater with the thermostat up full ( the sound like it is trying to impersonate a jet aircraft taking off )

 

[WillH]

Bart, is your thermostat is in the same place as mine, by the control panel? If so we have no problems with ours. Once up to temperature I leave it alone and the temperature is fine.

 

[two]

In simple terms I think there should be little difference in the amount of gas consumed to generate the same amount of heat (degree of comfort), whatever the method. There may be an optimum burn rate but I doubt there will be much variation either side and have no idea at what stage that might occur anyway. I think there are three jets within the boiler and these are modulated by the control board, so the amount of gas being burned at any time will depend on what the control board is programmed to do. I assume that it attempts to burn the gas in the most efficient way for the perceived demand.

The result of your experiment is interesting. I assume that you set different target temperatures for the two positions, to achieve a similar comfortable state? There may be a greater variance of the actual temperature at the higher level, due to air turbulence, and the gas burn may be a function of the gap between the actual and the demanded temperatures. Fan speed is, I believe, a function of the boiler temperature. With so many different factors influencing things, it is conceivable that some circumstances will produce a more stable operation than others. Did you not try an intermediate position? Somehow I don’t think a ground level position would provide as good a control.

Besides gas, you have the 12V consumption to consider as well. The amount of electricity consumed by the fan will add up and need top be replaced. There may not be much difference between thw two conditions you have described but I thought I’d add that to the mix, for consideration.

(Now I’ve rambled…)

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[Bart]

Bart, is your thermostat is in the same place as mine, by the control panel? If so we have no problems with ours. Once up to temperature I leave it alone and the temperature is fine.

Yip it is , and ive never been happy with the way it performed , if after moving it and im still not trully happy , then i think i will buy a new sensor and try it.

 

[Bart]

In simple terms I think there should be little difference in the amount of gas consumed to generate the same amount of heat (degree of comfort), whatever the method. There may be an optimum burn rate but I doubt there will be much variation either side and have no idea at what stage that might occur anyway. I think there are three jets within the boiler and these are modulated by the control board, so the amount of gas being burned at any time will depend on what the control board is programmed to do. I assume that it attempts to burn the gas in the most efficient way for the perceived demand.

The result of your experiment is interesting. I assume that you set different target temperatures for the two positions, to achieve a similar comfortable state? There may be a greater variance of the actual temperature at the higher level, due to air turbulence, and the gas burn may be a function of the gap between the actual and the demanded temperatures. Fan speed is, I believe, a function of the boiler temperature. With so many different factors influencing things, it is conceivable that some circumstances will produce a more stable operation than others. Did you not try an intermediate position? Somehow I don’t think a ground level position would provide as good a control.

Besides gas, you have the 12V consumption to consider as well. The amount of electricity consumed by the fan will add up and need top be replaced. There may not be much difference between thw two conditions you have described but I thought I’d add that to the mix, for consideration.

(Now I’ve rambled…)

Yip the fan uses about 5amps when on full pelt , and uses about 1amp when low , but ofc when low it is running for a lot longer.

As for trying a mid height for the sensor , there is nowhere suitable mid height , well without running a lot of cable , again i will experiment more over the next few days before i drill an actual hole for the sensors new location.

 

[Bart]

Bart, is your thermostat is in the same place as mine, by the control panel? If so we have no problems with ours. Once up to temperature I leave it alone and the temperature is fine.

Do you not have any problems keeping the mh luke warm ? As setting the thermostat at 5 for me heats it up ok but then after the fan stops the mh gets very cold before the heater restarts again , but if i try 7 then it keeps the mh to warm , and the fan on the heater is going full pelt for ages.

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[WillH]

We set it to 6.5 or 7, keeps the van warm. On 7 the van idles most of the time unless it's really cold,or windy. For sleeping we set it to 3 or a little under.

 

[WillH]

Just a thought but there is something we have done to improve things. When parked up we put our shoes in the front, under the dash. They are always cold. My wife has made a quilt that I peg to the tray at the bottom of the dash and tuck in at the doors. This has made a substantial difference to the heating performance. The quilt drapes down to the floor and stops almost all the cold air coming in, especially if we are nose into the wind.

 

[Bart]

Just a thought but there is something we have done to improve things. When parked up we put our shoes in the front, under the dash. They are always cold. My wife has made a quilt that I peg to the tray at the bottom of the dash and tuck in at the doors. This has made a substantial difference to the heating performance. The quilt drapes down to the floor and stops almost all the cold air coming in, especially if we are nose into the wind.

Thanks will maybe try something like this in the future , i never tried anything with the mh sensor today , if i get chance and weather permitting ill have another mess around tomorrow

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[tonyidle]

Yip this is what was happening , and the heater does not come back on until the MH is freezing.


Which fan is it that i hear when i first turn on the heater with the thermostat up full ( the sound like it is trying to impersonate a jet aircraft taking off )

That'll be the combustion fan. The blown air fan turns very slowly until it notices heat being produced - then it speeds up. It works like that to prevent cold draughts from the vents.

Truma heaters work in a slightly counter-intuitive way. At start up no gas flows. The combustion fan starts and blows air through a venturi creating a pressure drop that draws in gas to mix with the air - very like a petrol carburettor does. The faster the combustion fan spins, the harder it blows, and the more gas it draws in.

 

[Bart]

@tonyidle Thanks

 

[tonyidle]

In simple terms I think there should be little difference in the amount of gas consumed to generate the same amount of heat (degree of comfort), whatever the method. There may be an optimum burn rate but I doubt there will be much variation either side and have no idea at what stage that might occur anyway. I think there are three jets within the boiler and these are modulated by the control board, so the amount of gas being burned at any time will depend on what the control board is programmed to do. I assume that it attempts to burn the gas in the most efficient way for the perceived demand.

The result of your experiment is interesting. I assume that you set different target temperatures for the two positions, to achieve a similar comfortable state? There may be a greater variance of the actual temperature at the higher level, due to air turbulence, and the gas burn may be a function of the gap between the actual and the demanded temperatures. Fan speed is, I believe, a function of the boiler temperature. With so many different factors influencing things, it is conceivable that some circumstances will produce a more stable operation than others. Did you not try an intermediate position? Somehow I don’t think a ground level position would provide as good a control.

Besides gas, you have the 12V consumption to consider as well. The amount of electricity consumed by the fan will add up and need top be replaced. There may not be much difference between thw two conditions you have described but I thought I’d add that to the mix, for consideration.

(Now I’ve rambled…)

There are no jets within the boiler. See above. Boiler output control is achieved by modulating the combustion fan speed.

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[two]

Terminology? If there are no 'jets' within the boiler, how does the boiler heat?
I recall seeing what I thought were three jets in the centre of a cut-out version at the NEC show. I assume that was a Truma6 and that a Truma4 would have only two 'jets'.
I assumed that each could be switched on/off individually to control the output, maybe incorrectly?

 

[TheBig1]

Just a thought but there is something we have done to improve things. When parked up we put our shoes in the front, under the dash. They are always cold. My wife has made a quilt that I peg to the tray at the bottom of the dash and tuck in at the doors. This has made a substantial difference to the heating performance. The quilt drapes down to the floor and stops almost all the cold air coming in, especially if we are nose into the wind.

2 pieces of magnetic sign vinyl covering the bonnet vents helps keep the cab warmer and reduces the draughts. the other draught entry points are

vents under driver and passenger seat that you can buy plastic covers for or use duct tape

vents in the edge of the cab doors that can be taped over

the lower seatbelt holes in the cab are open to the underside of the van. push in some foam to reduce the draught