Owlpost #3: Bunny, the Boiler

I have forever had a weird curiosity about how things work. When I was younger I pulled apart old hifi systems (to not much enlightenment), and then tried the family piano which resulted in plenty of broken elastics and the ruination of the piano’s action (not my finest hour). Thankfully being Mr Curious is a useful bent to have when it comes to learning boat stuff and generally getting things fixed.

We have mentioned our diesel boiler before. I have christened her Bunny as she’s a total nutjob. This is her and this post is the hotly anticipated in-depth expose on her inner workings.


The last week has seen her increasingly unable to start-up. Like an old car on a freezing cold day, she needs to be kicked several times to make her go. This morning, we were unable to make her go by the time we had to leave for work, despite copious coaxing (priming of the fuel line). Dull.  Thankfully at least it’s not Baltic in London this week. It’s just half Baltic. Oh good. If you’re not remotely interested in mechanics the rest of this post will be seriously boring – rather like being cold at breakfast.

To be fair to her, last time we ran out of diesel I didn’t see it coming so she managed to hoover up all the crap and water at the bottom of the tank which made her cranky.  Since then it’s just got worse and worse, so tonight I spent several hours giving her the full once-over.

First a disclaimer. If anyone out there in internet-ville reads this and thinks it’s a good guide to them fixing their boiler, don’t even start. I am not a heating engineer. I claim no expertise. Bunny (and others like her) create a massive jet of flame using an arc of 10,000+ volts of electricity across a spray of diesel, so they aren’t machines to mess about with unless you have some important rules of engagement in place. If you follow my lead it’s on your own head. Call a heating engineer if you’re remotely uncertain. Disclaimer over. For those that have got this far, well done.

When we were first bringing Bunny to life I played apprentice to the excellent Mark Mead, a very fine marine engineer in these here parts. He gave me the basics of Bunny. Big red cabinet with water pipes in it and a pump on the back – almost never breaks. Blue box that spurts flame into it – plenty of ways to kill it. As our issue concerns the lack of fire, this is where the startup issue lies. I don’t know how to fix cars but I remember hearing a line in a film once that there are only two reasons a car won’t start – no fuel or no fire. I’m going for the same principal here. I know dirty diesel has been an issue so I’m aiming to scrub and flush and clean anything that moves fuel.

Taking the blue cover off Bunny’s frontal lobe reveals something a bit like Darth Vader without his helmet on.

cover off

Bottom left with the red button is a standard heating control box made by Siemens/Landis & Gyr. Top centre is a transformer that makes the lightening. Bottom right is a small motor that drives the fan (hidden inside) and also the Suntec fuel pump visible in shot. Four screws later, and the whole front section can be detached, which reveals that the back of Darth Vader looks a lot like a Dalek (no prizes for guessing what TV genre I favoured as a kid).


A close up of the end of the Dalek’s raygun reveals where the lightening happens: the two insect-like antennae above the brass coloured nozzle. the tip

That whole end of the beastie needs a good scrub down so I remove the wand, careful to mark how extended it is from the main chassis as that plays some roll in the combustion efficiency. Applying a little wire brush and some white spirit turns the shield bit from this to this…

dalek 1dalek 2

…and I also flush through the pipe that connects the pump to the wand…

pump pipe

So maybe the long nozzle is blocked but I’m hoping not as I can’t force white spirit down it. I also scrubbed the insect lightening givers a little, so all up, the delivery end for the fuel should be ok. Stepping back in the chain is the pump. This is where I know there has been a problem before. I pull the front face off the pump to reveal a fuel filter.

pump 1pump 2

I did give this a quick clean last week so it’s not too filthy. But I still give it a go with the wire brush and some white spirit to make sure it’s back to top cleanliness.


So this is as far as I’ve ever gone with pulling Bunny apart. I’ve never seen the moving parts of the pump and I this time I want to be very thorough. So keeping the piano incident from my childhood in front of mind, I step carefully on.

This the back portion of the pump, which connects to the external fuel strainer with two pipes, one input and a return for un-used fuel.

IMG_2625 IMG_2629

I have cleaned out the strainer a hundred times so I know it’s ok. But, just like Brad Pitt in Seven, what I don’t know is what’s in the box. To get the pump off I need to unscrew the transformer, unplug  the control box and detach the solenoid thing from the top of the pump which makes Darth Vader look a little bare.


Unscrewing the fuel lines from the strainer means I can detach the pump entirely from Bunny. And what do we find… Hmm. The big bolt on the side actually reveals an internal spring laden with garbage and rust. Joy. Also the bore that houses the spring is also not looking its finest.


So a little white spirit, brush and some ear buds get rid of all the nonsense and hopefully we’re back to full function. I don’t know what the spring does, nor the screw setting on the bolt that caps it so I’m going to leave it ‘as was’.

The last bits left to nosey into are the three screws on the front of the pump. Removing those reveals a very minimal set of gears. Clever! The photo is missing the centre cog but suffice to say there isn’t much to it. The crescent moon on the lower piece rocks around a central pin. The silver cog turns on the central drive from the motor. Basically I’m not enough of a mechanical engineer to know how this manages to move fuel, but it does. My brother Dave may well know the answer.


Piano destruction once again front-of-mind I clean everything up carefully and put it all back together again, which incidentally takes some doing as the pieces are machined very accurately. Luckily I also like a puzzle.

If you’re still with me, you’ve earned a bottle of vodka on your next visit.*

So, confident that I haven’t broken anything, I prime the fuel line and hit go… and absolutely nothing happens. In fact it’s worse: it’s not even trying to fire now. Hmm. Ok.

Apply logic: fuel or fire? There is a small viewing window in the front of the box to see whether it’s sparking, and it still is. I haven’t destroyed the electrics. A big tick for fire.

So, fuel… Did I break the pump? F$£k!!! At this point I did spent about half an hour swearing and trawling the internet for a manual. I found one that’s not exactly the same model, and then randomly another on a Polish website that is and is thankfully in English. From these I learn a few things.

It turns out the spring in the bore actually works with the solenoid valve on top of the pump to regulate flow. The screw on the cap actually controls the fuel pressure. Good! Turn the pressure up. Hit go again, and the motor doesn’t even turn. It makes a sound like it’s trying but can’t. BAD. I pull the plug quickly before it burns out and try not to panic.

More reading of the manual reveals that despite making sure I pulled it apart carefully, I may have put the fuel hoses back the wrong way round. Oh. I fix that and turn the pressure adjuster back down, and finally, with a sound like a large beast waking up, Bunny comes to life. In fact, she wakes in a far heartier fashion than I’ve heard her manage before: the low rumble of the fire sounds deeper and she starts up much faster. There was a lot of raucous whooping and dancing around at this point (yes I was on my own). In the immortal words of Charlie Sheen, we were now winning!

My final hurdle was the strainer which had long been intermittently making a horrid whining noise whenever it was running short of fuel. As a result of my recent ministrations it was now doing it continuously. Theory a) Maybe the pump was now too powerful. I wound down the pressure adjuster until the flame was extinguished, but the noise continued. Some time ago I had fitted a priming bulb on the fuel line to help out when we changed tanks. Turns out it (theory b) was strangling supply. So I removed that (jury’s out on whether we’ll need to put it back on) and our dear Bunny was back to her fire breathing best.

Mission accomplished.

*this is a joke. We expect everyone to find Bunny as interesting as we do.


3 thoughts on “Owlpost #3: Bunny, the Boiler

  1. Veronika Metcalf says:

    I almost had to scroll to the end as the suspense was killing me. Glad the ending was successful,O owl of many talents

  2. Joods says:

    I don’t believe it! Minky’s married her father! The very first time I met John A-J he gave me chapter and verse about how the Thames Barrier works! I was fascinated. Here Owl, oh so clever and wise, has taken me through a boiler service. Now, whereas it is easy to dismantle something you need to be dead clever to be able to put it all together again in the right order. What a genius. Yes, you must be careful not to let Bunny slurp up the gunge at the bottom. We were always advised to switch off before filling her up too. Let gunge settle before turning back on or yucky bits get sucked in. End of advice column. Lots of love you boatees. I’ll get to see it one day I hope!

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