Hot water draining back to holding tank

[LMC Camper]

Can anyone advise on how best to stop the hot water in my motorhome kitchen and washroom basins draining back into the holding tank ovenight?

 

In the morning, or after some hours without use, we find that both hot feeds have air in the pipes which needs to be opened for some time to get it out before the hot water arrives.

 

The system is a Truma C6002 combined water/air heater with an electrical safety/drain valve installed close to the Truma unit, there is also the main drain valve in the same area.

 

Can I fit a simple one-way valve (or valves) in the system to prevent this drain back?

 

If so where is best to fit it? - and how do I make sure that I can still drain the whole water system in winter?

 

Any hints and tips would be greatfully accepted so that we can have a hot wash without the wait for water to heat up in the Truma unit!

[Brian Kirby]

To be clear, do you mean water actually in the sink and washbasin, or water in the tap feeds, is draining back?  It's just that you say holding tank, which I understand to be the waste tank, but I think you may mean the fresh water tank?

On the understanding it is water in the tap feeds that is draining back into the fresh water tank, the problem is that the non-return valve (NRV) on the main feed from the fresh water tank (which feeds both hot and cold systems) is either stuck open by grit or limescale, or has failed.  I strongly doubt this has anything to do with the water heater itself.

If your van has a submersible pump, that you can see sitting near the bottom of the fresh water tank, it is probable the NRV will be integral with the pump.  Try carefully, but energetically, shaking the pump while in the tank, to rattle the NRV about as much as possible.  If it is jammed, this may free it.  Then test.  In this doesn't work, you'll need to remove the pump from the tank (may be a fiddle!) and try flushing it under a tap in your home.  If you can hear a rattle when you shake the pump, it should mean the NRV is free.  Re-install in the tank and re-connect to test the result.  If it still lets by, the NRV is US and you'll most probably have to get a new pump, as the NRV is likely to be integral.  Otherwise, if the valve can be replaced, simply replace the valve.

If the pump is not of submerged type, there will be a NRV in your system at the pump, possibly integral with the pump, or in the feed between pump and fresh water tank.  What you need to do next, will depend on what is where, and what kind it is!  Manual time!

[LMC Camper]

Brian - thanks once again for the quick and helpful reply.

Must get my technical terms right when creating the posts!

The water is indeed draining from the tap to the fresh water tank.

My LMC has a pump built into the top of the tank and so I'll unscrew it and give it a clean out. It is easy to get at so should not be a problem.

 

The motorhome has not been used for over a year as it was a finance reposession. So we got a low mileage bargain but the long layup has obviously taken its toll on some mechanical parts.

 

The heavy german manual is full of nice photos and 'how to clean' information but technical advice is sparse to say the least! So your advice is much more helpful than the manual.

[Brian Kirby]

Well, lets just hope you can as easily work out where the NRV is hidden, and fix the problem!

[LMC Camper]

Hmm... as suspected the NRV is built into the submersible pump and it only partially works.

 

New german deluxe pump is £25 but one way valve is £3 - no contest so I'll install it next to the pump top with a couple of jubillee clips.

Thanks for the assistance.

Ian