We planned maintenance on the (Quick Nautica 20BX) boiler in Molia this season because it has been making scolding hot water! This included: checking the element and its anode – did you even know there was one in there? Then checking the cylinder for scale, and adding the thermostatic valve kit from Quick to keep the hot water temperature reasonable.
Step 1 – Drain or switch off the water tank, undo the electric connections, boat disconnected from the mains obviously! Then disconnect the water and engine coolant, and remove the boiler from its holding straps.
It will be still about a third full at this point, and heavy. On Molia it only just fitted out through the locker with the cover off. (The locker cover is also the double saloon bunk base.)
Step 2 – give the locker a good clean!
Step 3 – empty the last water out. I removed the boiler to my workshop to make the next few steps easier.
Note that I had to cut the engine coolant pipes off just at the ends of their connectors. This was because they had fused on over the years! I removed these in the workshop.
Step 4 – With reference to the diagram (below, left). Remove the cap (12) and electrical connections (11,14), and then pull out the thermostat (10). The supply wire earth is attached to the cylinder earth post with a nut and washer (13,14,15). The thermostat itself is not attached with any screws – it is just clipped into the element head.
Step 5 – Getting the element out! This looks easy from the maintenance diagram in the Quick Manual (above, left), but it is not! You will need a specialist 55mm element spanner (above, centre) as the element head is recessed into the top of the cylinder.
Our old element is completely missing its anode (above, right, foreground) and there is scale and corrosion around the anode stub and the main element thread. It is possible quite cheaply to replace the anode alone; but due to the age of our element, and the scale and corrosion, I decided to replace the entire thing.
The element rating is moulded on its end – ours is 1200W. Thanks to Force4 for their fast supply of a replacement element (above, right, background).
I inspected the inside of the cylinder itself with a torch, and it did not show too much limescale. So I just washed it out a couple of times.
Step 6 – refitting the element. Don’t be fooled if the element kit contains two seals. Check the old element connection – it either uses the O-ring or the gasket supplied, not both. Ours uses the gasket. Tighten the new element into the cylinder.
Step 7 – Fitting the thermostatic valve kit – again not as easy as the diagram suggests! The threads on the cylinder’s hot and cold water connectors are aligned so that the valve (1) and T-connector (5) finish up pointing away from each other when fully tightened. This makes the supplied flexible hose way too short.
I solved the plumbing problem with a speedy trip to Screwfix, for a longer hose and extra male hose connector.
Step 8 – reconnect the water. Back on the boat, the push-fit pipes were easy to reconnect without any leaks. The new brass connectors were much more difficult to get leak-free – they needed both (don’t tell your plumber) PTFE tape and jointing compound! Leak testing needs the water filled up again (or turned on), and pressurised.
The engine cooling pipes, reconnected with their jubilee clips, proved to be leak-free first time when tested.
It was at this stage that I reattached the cylinder’s holding-down straps.
Step 9 – reconnect the electricity and replace the plastic cap over the end of the thermostat. With the water and electricity back on, check the element heats the water.
Step 10 – check the engine coolant level. Depending on how much coolant was lost during disconnection and reconnection of the coolant pipes at the cylinder, it may need topping up. Run up the engine so that the coolant is pumped through the cylinder to check for leaks. Stop the engine and allow the coolant to settle, check the level again.
Before (left) and after (right) showing the installation of the thermostatic valve kit, and everything else connected.
A note on electrical safety: depending on your experience and qualifications, you may want to employ a professional for the electrical connection and checking steps described here.