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Canal Boat - - This Month -

So­lar pan­els, bow thrusters, air­locks in the heat­ing, and an en­gine that some­times just dies

Q I have re­placed the ra­di­a­tors (and added an ex­tra one in the bath­room) on my Alde 2928 cen­tral heat­ing sys­tem. Af­ter re­fill­ing with 50-50 water/an­tifreeze I bled the sys­tem thor­oughly and tested it. The bed­room and bath­room ra­di­a­tors (both to­wards the stern) get hot over the whole sur­face area, but those in the cen­tre and front only get hot at the bot­tom half; the top stays al­most cold. The pump is work­ing, and the sys­tem con­nects through the calori­fier as well. Is there an air­lock some­where? How can I fix it? ANDY OXLEY, via email A TONY REPLIES: As hot­ter water will rise, the bot­toms of the ra­di­a­tors can­not get hot while the tops stay cold un­less they ei­ther have air in the tops or the an­tifreeze was not first mixed with water (hot an­tifreeze is denser than cold water). I won­der if those ra­di­a­tors did not drain when you worked on the sys­tem. You could try turn­ing the boiler ther­mo­stat (the knob with num­bers on it) up to max­i­mum and do the same with any room ther­mo­stat. Then run the boiler for sev­eral hours. The dif­fer­ent water flow paths through the dif­fer­ent ra­di­a­tors just might mix it enough.

I know you have bled the sys­tem, but as most boats are trimmed slightly up at the bows, any air may have been driven into the ra­di­a­tors at the front.

If you are ab­so­lutely sure you mixed the water and an­tifreeze be­fore fill­ing, try bal­anc­ing the sys­tem. An in­ter­net search will give you at least two dif­fer­ent ways of do­ing it but ba­si­cally you ad­just the lock­shield valves (the ones that are not eas­ily ad­justable) so all the ra­di­a­tors get the same flow. This may mean clos­ing the ones clos­est to the boiler a lit­tle and open­ing the ones fur­ther away. The calori­fier is nor­mally piped into the sys­tem in the same way as a ra­di­a­tor but it may only have an ad­justable valve on the in­let side some­where: make sure this is not fully open. 1. Diesel-fired heater, hot flow pipes red and the cooler re­turn pipes blue 2. Op­tional ser­vice valves 3. Twin pipe header tank 4. Calori­fier 5. Iso­la­tion valve 6. Lock­shield valve. Used to bal­ance the flow through each ra­di­a­tor 7. Ra­di­a­tor 8. Ther­mo­static ra­di­a­tor valve (TRV) 9. Towel rail 10. Pipework

TIP: Flow rate is para­mount to get­ting the best out of your heater and sys­tem. Don’t fit too many el­bow fit­tings in the pipework, al­ways use swept bends where pos­si­ble. Oddly, when bal­anc­ing your sys­tem don’t be afraid of re­strict­ing the flow through the last ra­di­a­tor. Be­cause of the pipe lay­out in a typ­i­cal nar­row­boat, it is nor­mally the mid­dle ra­di­a­tors that suf­fer from lack of flow, not the be­gin­ning and end ones. If your last ra­di­a­tor has been plumbed prop­erly you will be able to slow the flow down and force more water through the mid­dle ra­di­a­tors. Al­ways keep the plumb­ing side a sim­ple as pos­si­ble, have one main flow and re­turn in 22mm pipe and tee all the com­po­nents off in 15mm.

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