Tony323 Posted November 21, 2021 Share Posted November 21, 2021 Hi all,having never put the gas heating on alone without heating the hot water, as come winter and the van on the driveway, it was getting a bit too damp, so thought i would put the gas on without heating the water. So i tested the water, after 5 min. Turning the cold water on, it came out luke warm for 30 seconds, then cold after that. Is that normal. I checked the settings by the manual. Is it that the hot blower pipes are close to the water heater ?? Link to comment Share on other sites More sharing options...
colin Posted November 21, 2021 Share Posted November 21, 2021 Guessing that you might have a Truma Combi, when used on heater only the hot water tends to also heat up a bit, as to why your cold gets some heat, I would guess the cold water pipe goes near the heater or one of the air ducts. Link to comment Share on other sites More sharing options...
rayc Posted November 21, 2021 Share Posted November 21, 2021 it is normal. If you have water in the boiler and select space heating only then the water will get warm / hot as the water due to the design. The heating and water share the same electrical elements or gas burners which are around / below the water jacket.. The heat of the water will not be controlled as in the case of selecting water heating. Link to comment Share on other sites More sharing options...
Tony323 Posted November 21, 2021 Author Share Posted November 21, 2021 Hi Colin and rayc, thanks for your input, i thought maybe the same that pipes are so near , with water in it, it is making the water go luke warm, really i was just bothered about, is that if had no water in the Truma Combi, that putting the heating on with controls set as per manual, it would damage the boiler. Link to comment Share on other sites More sharing options...
rayc Posted November 21, 2021 Share Posted November 21, 2021 Tony323 - 2021-11-21 12:06 PM Hi Colin and rayc, thanks for your input, i thought maybe the same that pipes are so near , with water in it, it is making the water go luke warm, really i was just bothered about, is that if had no water in the Truma Combi, that putting the heating on with controls set as per manual, it would damage the boiler. It is a function of the design that the heating can operate whilst the boiler is drained as long as the space heating only option is chosen. If water is in the boiler and space heating only is selected then the water will get warm/hot by conduction. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 21, 2021 Share Posted November 21, 2021 Tony323 - 2021-11-21 12:06 PM Hi Colin and rayc, thanks for your input, i thought maybe the same that pipes are so near , with water in it, it is making the water go luke warm, really i was just bothered about, is that if had no water in the Truma Combi, that putting the heating on with controls set as per manual, it would damage the boiler. The Combi is designed to be used for heating only (i.e. dry, with no water on board). Unless you have your van in frequent use (for camping, not shopping) it would be prudent to drain out all water, including any in the Combi, as the greater potential source of damage at this time of year is frost. This applies equally to water in the pipes from the fresh water tank to the taps, shower, and the Combi itself. Should water in the van freeze it has the potential to split the Combi water jacket, the pipe connections, the pipes themselves, the taps/shower control, and the water pump. For this reason the pump should be left "off" and all the taps and shower controls left open (if mixers, in mid-position between hot and cold). If the toilet has a separate flush water supply also drain this. Any water left in the van, although it will have been chlorinated at the time of filling, will lose its chlorine content over time, becoming prone to developing potentially harmful algae. Adding fresh chlorinated water will not be sufficient to kill the algae, so best practise is to drain everything down, only filling when the van will be used, and draining down again as soon as possible after each use. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted November 22, 2021 Share Posted November 22, 2021 The relevant part of Truma's operating instructions for "Combi" heating appliances is attached below. As advised, when 'Heating Mode' is selected "If the water container has been filled, the water is automatically heated as well. The water temperature depends on the selected operating mode and the heater output". Operating a Combi in Heating Mode for 5 minutes on gas will cause the appliance's internal heat-exchanger to transfer a quite small amount of heat to the water in the appliance's water container, and that heated water will naturally rise into the upper section of the water container. I'm not sure about the wording of Tony's original posting, as - if a COLD-WATER tap is turned on - it should just deliver cold water. But if a HOT-WATER tap were turned on after the Combi had been operating for 5 minutes, there would be a brief flow of slightly warm water followed by a continuous flow of cold water, exactly as he described happened. Regarding putting a Combi into Hot Water Mode with its water container empty, plainly this would be a perverse thing to do deliberately, but could easily be done accidentally. I don't know if a Combi has any 'interlock' that would recognise that the water container was empty and prevent the Combi from operating, but I'd guess not. I remember (20 or so years ago) asking a Truma technician about the effect if a Trumatic C combination air/water heater were operated in Hot Water Mode with no water in it. I was told that - with no water in the container as a 'heat soak' - the heat-exchanger would heat up the metal of the water container very quickly and the thermostat on the container's metal surface would shut the appliance down. I asked what the chances were of the water container becoming damaged and the technician believed the risk was small. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 22, 2021 Share Posted November 22, 2021 Further to the above is the following, copied from a bit further into the Combi instructions (and applicable to the Combi (E) - in our case, a Combi 4 (E)). However, it would be wise to check the instructions (in our case dated 02/2017) for your Combi, in case of variations. "Combi The interior can be heated either with or without water, depending on the setting. Combi E The interior can be heated in gas, electrical or mixed mode, either with or without water, depending on the setting. Check whether the power supply fuse protection at the camp site is adequate for the 900 W (3.9 A) or 1800 W (7.8 A) that have been selected using the power selector switch. The cable drum must be fully unwound in order to prevent the power cable from overheating. – Check to make sure the cowl is unobstructed. Be sure to remove any covers that may be present. – Open the gas cylinder and the quick-acting valve in the gas supply line. – Fill boiler with water if necessary (see “Filling the boiler”). – Switch on the unit on the control panel. Switching off – Switch the heater off on the control panel. – The switch-off procedure may be delayed by several minutes because of internal heater operations. Always drain water contents if there is a risk of frost! If the appliance is not used for a long period, close the quick acting valve in the gas supply line and the gas cylinder." Link to comment Share on other sites More sharing options...
Derek Uzzell Posted November 22, 2021 Share Posted November 22, 2021 Tony's motorhome is a 2011 Hobby Toskana 690, so the heater is likely to be a Combi 6E. The significant thing about the Truma instructions just quoted is that they relate to interior heating. In the 'mode' attachment I provided Truma just refers to this type of operation as "heating" - though I'd call it "blown-air heating" to differentiate it from water heating. There's minimal potential risk of damage when blown-air heating is in operation and air is passing between the Combi's heat-exchanger and its water container, as most of the heat produced by the exchanger will be transferring to the air. If the Combi has water in it, heat from the hot air will gradually begin to heat up the water as a 'by-product' of the air-heating. If the Combi does not have water in it, heat from the hot air will heat up the empty water container, but the air passing between the Combi's heat-exchanger and its water container should prevent the container becoming excessively hot. Link to comment Share on other sites More sharing options...
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