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Posted: Sun Nov 01, 2009 6:04pm

Post Subject: Winterisation

Can someone please advise me how best to drain down the domestic water system. Thanks Duncan

Tony-B
Tony-B

Posted: Sun Nov 01, 2009 7:09pm

Post Subject: Winterisation

Dear Duncan, in short NO. Unless special provision has been made to do this during construction it is highly unlikely that you can totally drain the domestic water system. There will always be low points, possibly under the floor where water will remain. On modern boats with plastic plumbing this is not such a problem because the plastic usually gives enough when the water freezes and many boaters never drain their system down. I must say that last winter I was getting a bit concerned but the boat was fine with a full system. You will find that much of the plumbing is below the waterline so heat from the surrounding water helps to prevent the plumbing freezing. It is VITAL to drain the diaphragm chamber on instant gas water heaters and it would be a good idea to drain or remove an expensive shower mixer valve. You should also leave all the taps open and the water tank less than full so there is space for ice to expand. If you want to drain down the system (as far s it will)pump as much water as will come out of the taps etc. whilst running the engine to ensure the batteries are not discharged. Remove the hot water outlet and the cold water inlet from the calorifier and drain that down. Follow any instructions for the toilet. Drain any instant gas water heater, the shower mixer and domestic water pump. Mix a 50% antifreeze mixture in a bucket, get someone to hold a bucket under the shower outlet, operate the shower pump whilst pouring the mixture into the shower waste until coloured water comes from the waste. Dispose of the antifreeze mixture responsibly. Remove the filter bowl from any water filters. However in most years you stand a very good chance of not having to do it. Tony Brooks

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Posted: Mon Nov 02, 2009 9:44pm

Post Subject: Winterisation

Tony, Thanks for the advice. I have one question, if I turn off the inlet to the water pump from the water tank will I be able to pump out the water in the system as you suggest. Duncan

Tony-B
Tony-B

Posted: Tue Nov 03, 2009 9:03am

Post Subject: Winterisation

Dear Duncan, Why would you want to do that? If you are worried about pipes freezing what about the water tank if its left full of water. The pump has to be able to suck something in so it can then blow it back out. If you turn the main valve off the pump will not be able to suck anything so it will not be able to deliver anything. If you leave the valve open the pump will suck water out of the tank and when the tank level is below the outlet level the pump will try to suck air. It will not be very efficient at that but it will probably bubble air through the pipes but not enough to blow all the water out of them. The only time doing this would be ill advised is if you are using a Jabsco type flexible impeller pump when care is needed to minimise the time it runs without water inside it. Tony Brooks

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Posted: Tue Nov 03, 2009 8:52pm

Post Subject: Winterisation

Tony, I was concerned that if I sucked air into the system I may create an airlock or have problems primeing the pump after refilling the water tank. Duncan

Tony-B
Tony-B

Posted: Wed Nov 04, 2009 9:37am

Post Subject: Winterisation

Well, lets assume you did not draw any air into the pump - what will the pump use to "push" the water in the pipes out? If you are worried about the winter then you need to get as much water out of the pipes as you can (but as I explained above you will not get it all out). Now, you could send pounds on potable antifreeze or even fill the tank with alcohol (Vodka!), drain the tank, fill with said antifreeze or alcohol and pump that through the system to expel the water but unless you have a centrifugal water pump (probably dating from the 1960s called a Godwin) your pump will be self priming and once it has primed it will use water to expel any air in the system. Getting an airlock is about as likely on a boat as getting one in a house on the system connected to the rising main. It may take a while for the last bit of air to be expelled but unless you have an appalling plumbing layout get expelled it will. Even if it did not it would only tend to act as a small accumulator. You can not drain a water system down without allowing air into the pipes. Tony Brooks

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