Water Pump staying on!

[Ringy]

Hi, with the colder weather forecast I thought I should drain the Motorhome. Opened the valve for the fresh water and it drained away ok. Then flicked the yellow switch beside the water boiler and saw it drain away (looking at the external outlet) as expected. Also opened the hot water taps in the kitchen and loo - water stopped coming through the taps quickly but took a while to stop draining outside. However while no more water is draining the pump remains active. It’s an old van (2004 CI Carioca) so I doubt there’s any low-temperature related switch on at play here. I’ve double checked all taps are off, and had a look in the fresh water tank which is also empty. I’ve tried flicking the yellow switch, but pump is still running. It goes off (of course) when I switch it off at the control panel. Any thoughts chums?

 

[Aeron]

Sounds normal to me. The pump pressurises the water system so it is bound to keep running when there is no water to pressurise. Also, it should not be left running when the system is dry for too long as it will damage the pump. Pump needs to be switched off at the panel and not put back on until you refill with water.

 

[Gerby]

as said above, just sounds like a pressure activated system (as pressure drops pump starts) so you would naturally just leave the pump turned off until you refill the system in the spring.

 

[Ringy]

Gerby and Arron - thanks so much. Makes perfect sense. I’d watch a couple of YouTube videos about prep for winter, and don’t recollect any mention of switching the pump off. One mentioned leaving the tap open, to combat air blocks.....but could this also balance the pressure and do not activate the pump? Apologies if that sounds absurd, but I did fail my Science O Grade. !

 

[Aeron]

It is likely a sealed/pressurised system, so the pump will build up the water pressure until the system is 'full'. When you open a tap, water is released and so the pump starts up to replace the lost pressure. Leave taps open but switch pump off in winter when the system is empty so that any water left can have room to expand if it freezes but best not to have any water in there. As said previously running a dry pump for too long will damage it.

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[Gerby]

If you have winterised the van always leave the taps open as any water in the taps that freezes will cause damage.

Most vids showing winterisation would probably assume the pump was turned off as a matter of course due to the van being left unattended.

Aeron you beat my about 30 seconds.

 

[Ringy]

Thanks for this - understood!

 

[Aeron]

There should also be a small filter attached to the pump. This is a small glass/plastic bowl (about 2 inch diameter) with a metal filter in it. Unscrew the cap and empty the water out of that as well - just in case!

 

[pappajohn]

When the tank has water the tank side of the pump is under atmospheric pressure (14.7psi)
The outlet side of the pump is under pressure.... Say 20psi as an example... When the taps are off.
Open a tap and the pressure at the tap drops to 14.7psi thus turning on the pump via the inbuilt pressure switch.
Close the tap and the pump will build pressure until it reaches 20psi then the inbuilt pressure switch turns off the pump.
With no water in the system the pump can't reach 20psi so continues to run.

As its a diaphragm pump it won't do any harm running without water.
There is no internal impellor to be damaged by running dry.

 

[Ringy]

Aeron and Pappajohn - thanks again!

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[RobbyMClark]

Aeron and Pappajohn - thanks again!

Ditto from me too as noticed that last time in van and was going to try and sort at weekend.

 

[autorouter]

When the tank has water the tank side of the pump is under atmospheric pressure (14.7psi)
The outlet side of the pump is under pressure.... Say 20psi as an example... When the taps are off.
Open a tap and the pressure at the tap drops to 14.7psi thus turning on the pump via the inbuilt pressure switch.
Close the tap and the pump will build pressure until it reaches 20psi then the inbuilt pressure switch turns off the pump.
With no water in the system the pump can't reach 20psi so continues to run.

That's a good description of how it works, with the minor point that the pump output pressure is 20psi above the input pressure. So it's 20psi above atmospheric which is 14.7psi, so that's 34.7psi absolute.

 

[IRHP]

Normal as everyone has said. Your pump is trying to compress the air in the system instead of water.

 

[The Wino]

Maybe you had a different system before with microswitches on the taps. You would expect the pump to stop then with all the taps off but I think those systems are pretty unusual now.