Water heater replacement

In November I noticed that the bilge pump was running a little more frequently than normal.  After a little investigation under the sole, I could see a wet path leading from somewhere around the aft quarter berth area.  I removed everything from there and lifted the cover over the space under the bed.  I found some pooled water under the heater.  The heater still worked, and the water pump did not cycle often, so the hole had to be small.  Time to add another project to the list to be done before we leave. I swear that the longer we stay the more turns up 🙂

The existing tank was boxed shape and so did not lend itself to good use of the space available as the natural curve of the hull dictated the space under the bed.  I wanted to be able to use the space around the heater for storage.  After much investigation I chose a cylindrical IsoTemp SPA 11 gallon heater.  It is 15.5″ in diameter and 25″ long so it would just fit under the bed, and would be able to be pushed further towards the foot of the bed, creating more space for storage.

The weekend after the heater arrived, I set about the task of replacement.  First I turned off the water pump and disconnected the Pex tubing that supplied the water heater from the main water supply manifold.  I attached a stub of Pex with a valve on it so that we would turn the water back on while I was doing the work.  I then drained the old heater as much as I could via the drain valve.  I put towels down while manhandling the box out of the hole and off the boat.  The rust that had settled in the bottom of the heater was the last goop to come out and it left the space in a messy state!


Notice the outline of where the heater was mounted.  It was not possible to put much behind it as the heater almost came up to the top of the space.

I inspected the old heater and it turns out that it was made in 1993 and so was original to the boat.  Not bad going really.  I will be happy if the new one lasts that long.


I cleaned out the space and found that the bilge coat which was below the waterline, but on the hull itself, was peeling off in sections.  The space was warm when the heater was on, and this combined with the condensation in the colder months, must have let moisture get under the paint and caused it to peel off.

I sanded down the whole area, removing all loose paint and drilled 5 x 1.5″ holes in the forward wall close to the roof of the space.  I hoped that these would allow some degree of ventilation so that the warm air could escape into the vented cupboard that housed the air conditioning for the aft berth and head.

I bought the necessary fittings to go from the heater connections to the Qest fittings that were there already.  I slid the new heater into the space and marked on the inboard wall where the mounting bands would go.  I chose the wall as opposed to the floor for securing the heater as I wanted to make sure if there was any moisture build-up under the heater, no part of it would be touching the water.  Everything was then removed from the space and three coats of EZ Bilge applied.

I then mounted the bands on the wall and slid the heater into place.  The bands ran through the mounting feet and therefore could be rotated to place the tightening bolt anywhere around the heater.  This simplified the securing of the heater.

Once secured, I trimmed the Pex as all connections on the new heater were on one end unlike the old heater.  I did the same for the engine coolant pipes and the power supply cable.

With the plumbing and the electrical hookup done it was time to test the unit.  I reattached the supply tubing to the water manifold and turned the water pump back on.  There was a very small leak between the mixing valve and the heater body itself.  Once that was cinched up I left some kitchen towel under the heater and left it overnight to see if there were any others.  The next day the towel was still dry so I replaced the lid and left it running for a few days.  I wanted to see if the space got warm again.

When I reopened the space I could see that it was cooler than it used to be, probably a combination of the venting holes and better insulation on the new heater.  I also noticed a pool of water under the fittings… aaaarrgghh!  It turns out that this leak only showed itself when water was being pumped through the heater i.e. when the hot water tap was turned on.  Nothing showed when sitting under pressure alone which is why the overnight leak check bore no fruit!  When attaching the Pex cold water supply line, I did not bottom it out in the heater fitting before securing, leading to a poor connection.  Once this was fixed there were no more leaks to be found.

Needless to say this space has already been filled with “stuff”.  The picture below was taken just before that happened.




5 thoughts on “Water heater replacement

  1. Alan Bradley

    Nice job! I had to replace my original water heater, just like yours but installed in 2008. I too chose the Isotemp SPA 11. I’m hoping the stainless unit holds up better than the aluminum original. I took the opportunity to add shutoff valves to the cold inlet, hot outlet and to the coolant hoses from the engine.

    1. solpurpose Post author

      Alan, not a bad idea. My thinking was that if the first heater lasted for 21 years, I would not have need to unhook it before I sell the boat 10-12 years down the line.

  2. callingnoah

    gotta have hot water. i am really enjoying reading ‘the wanderer,’ moray. thanks for recommending when we met at jennifer’s birthday gathering. smooth sailing!


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