Hi Folks, I have a challenge with a Main Eco Elite 30 Combi which is short cycling on the CH. Water works fine. As soon as you have call for heat, the boiler fires up, modulates, but jumps very quickly (about 30 seconds or so from 40'ish all the way to 70, burner disengages putting it the boiler into its 3 min cycle for it only to repeat. Radiators upstairs heat up (moderately but not optimal) with downstairs stone cold. 9 radiators in total. Was advised originally that a powerflush was required. 2 x full circuit powerflushes, plus a boiler flush on its own. The main heat exchanger was also removed by the engineer and manually flushed, followed by a powerflush directly (as thought it may be blocked) CH Return flow pipe still does not get up to temp as the short cycling is probably not allowing heat to circulate all the way round the circuit as a result of the short cycling? The following have already been changed CH temp sensor Diverter valve Pump DHW plate exchanger DHW temp sensor Pretty frustrating as the boiler still short cycles. The interesting thing was when the boiler inlet outlets were connected to the powerflush and boiler switched on, still seemed to short cycle, even with a decent powerflush flow. The only thing which has not yet been changed is the inlet assembly, could there possibly be a block between that and the main heat exchanger? Any thoughts please. PS, yesterday when the DHW engaged, almost felt as hot water was being let off into heating flow pipe, Engineer swapped out replaced diverter for a new one this morning , but it has not resolved the situation. As a next step, the Engineer is now wanting to do a second powerflush of the boiler alone with some chemicals (ferrnox f2 )and run that for an hour or 2 as he thinks the main exchanger may be scaled up?) Any thoughts or ideas please.... Al
Short cycling is invariably caused by the inability of the system to remove heat away from the heat exchanger fast enough. The internal thermostat kicks in shutting off the boiler. you seem to have seen to most areas that cause poor flow bar a full power flush. A boiler connected directly to a power flush system is likely to short cycle, as apart from the volume of water in the system, there is no mechanism to loose heat sufficiently and fast enough. BTW - what pipe size is the CH using ? Is it a sealed or vented system ? Did you try altering the pump speed (may not work for vented system)
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