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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.