I understand Webasto's point of view though. It is quite common that a replacement given under warranty is guaranteed only for the remainder of the original warranty period, the warranty period does not reset. If you pay for another heater, you will have a full 5 year warranty. As a consumer, this is annoying and not "best in class" customer service but it is quite common. I actually give them high marks for replacing it so many times already. (Porbably not what you want to hear, but it's just my opinion)

Cheers, good luck

Steve

Is a mains electric heater fitted to the boiler? If so, have you checked the wiring, particularly the earthing arrangements, for this? Is there any electric circuit (wires or fixing brackets etc) between the boiler and the engine for instance?

I have now had 2 boiler [calorifier failures. The first on my Hanse 301 when it was 12 years old. I stripped the calorifier and found the leak in a Silver Soldered [Brazed maybe] joint alowing fresh water leak. I was able to repair the failty joint. The general construction was good with stainlees materials [Inox]. I believe the new owner has had another fail which would be 6 years from my repair but I'm not aware of nature of this fail. The Calorifier was fitted with a magnesium anode in the fresh water which was 30% depleted. No expansion tank fitted.

My second Calorifier fail on my 2007 315 was a corrosion related fail/leak  after 12 yrs under the rubber gasket that seals the flange. The calorifier is an IsoTemp 20l "budget" model. The tank is mild steel with vitreous lining, fitted with a large magnesium anode approx 30% depleted. The design is typical of Ilalian made boilers sold widely for domestic use in France, using mild steel for pressure vessel with vitreous enamel lining. I have knowlegde of these French Italian boilers [Chauf Eau], they often fail in < 10 years and you can visit any plumber in france and see a large pile of them in his scrap.

In my 315 the IsoTerm budget was fitted with 6 bar pressure release valve of poor quality, no pressure expansion tank was fitted so as the water heats and the pressure rises till it blows off vents. My PRV never vented to my knowledge. This cycling of pressure in a vitreous lined pressure vessel may cause fail/crack of liner. French Chauf Eaux boilers are usually limited to 3 bar.

I am fitting a new Calorifier from Surejust [all stainless of good quality] who say its imprtant to fit Expanion tank and their PRV is set to 4 bar and pressure vessel is Stainless. I hope and expect better life from this boiler.

From a manufacturers point of view this life may be acceptable, from owners with a bill for >£500 for boiler alone plus the  problem of failure at sea, high labour cost for difficult replacement, I feel this use of less than optimum materials and build quality is akin to the many builders who still fit poor seacocks and say change them often?

Just a further thought I have recently fitted a new domestic Calorifier in my house its made of Duplex stainless steel, this grade is better in this application than 316l grades [stronger and weldable without post weld heat trealment, not subject to stress corrosion cracking etc]  and is becoming standard in these and domestic applications.

Perry

My Isotemp manual has the following comment

Quote

Important! The water heater shall be connected to the mains power supply only when it is in service.

When leaving the boat for any length of a period, it is recommended to pull out the cable connector

from the socket to also disconnect the earth protection. This should be done even if the

shore power system is shut off, as there can be a potential difference, between the earth from shore

and the sea water earth of the boat. This can seriously damage, by stray current corrosion, the immersion heater, water heater tank or the engine with its drive unit.

Installation of a insulation transformer in the shore power equipment eliminates the risk of galvanic

corrosion via the shore power connection.

Unquote

That is obviously not very good advice if you are a liveaboard.

I actually do follow the recommendation and even though my yacht does have a galvanic isolator I do take it off shore power for the 2-3 week sessions when I am not on the yacht and the yacht is based in the cold Scottish environment, so corrosion rates are lower..  In the winter the yacht is out of the water.  As previous posters have said, we have to put up with the fact that some equipment is not really designed for the life of the yacht, as so we have to take every preventative measure possible.

Just one thought, though it is not normal practice to completely isolate components (ie break all 3 wires including the earth) when switched off, perhaps in this instance it may be worth considering.  

Thanks for that.

My H301 spent most life on an isolated mid stream mooring. Very rarely plugged into a mains. The 315 is often in marina. Both have galvanic isolators, but that doesnt help if there is earth leak current.

The 301 calorifier was clearly a deficiency in Braze/build quality. The 315 is an Isotemp buget model as I said using mild steel pressure vessel with vitreous enamel lining, the rust [and there was a lot of rust] was in beween the rubber gasket, the pressure vessel, and the header that holds the immersion heater and the thermocouple pocket for the dual over heat sensors. The magnesium anode was pretty big and only part used. I doubt if galvanic action was the cause, I have seen similar failures on French Domestic boilers, that use this mild steel pressure vessel protected by vitreous enamel coat.

This evening was speaking to a yacht chandler friend, who said his experiece of Isotemp boilers and many other calorifier manufacturers  was a 10-15 year life.