Its very difficult to get a good reading in the heat pac due to restricted space but initially it actually seems to rise a little but I suspect this is because the boiler flow pipe turns down immediately where as the boiler return goes out the side of the boiler and then very gradually rises so I think the boiler contents are inclined to "circulate" back through the return. The cycling time matches ~ the rad heat demand but its not that simple as the boiler once it cuts back in when the stat reaches ~ 60/65C has to reheat say 20/25 litres of boiler water from ~ 40c to its cut out of 70C so requires ~ 0.9kwh which takes ~ 2.7 minutes from a 20kw boiler. In general, once other rads are brought back on line then the % firing time does reflect the heat demand.
Thanks for that! I just can't help thinking my boiler Is cycling alot and probably wasting alot of heat up the flue whilst doing so. It's following the stat too closely. Hence why I believe a Boiler Energy Manager will greatly help my system efficiency. They monitor the flow and return temps and calculate the load on the system, controlling the burner.
I can't find any information on that Vector Group item I purchased from fleabay. From what I read they cost about £1600 - £2k from the company but someone on ebay with good feedback etc was selling a new unused one for £30 Inc postage
I'll open it when it arrives and see if anything is labeled and what sensors I would need. But may not be able to use it myself if nothing is labeled inside and its only meant to be fitted by them so looking at other BEM systems for Domestic boilers at present.
Plan is:
Balance all rads precisely and see if I can get return temps down
Meter the burner etc at 26kw setup and run for a few days.
Then downsize nozzle and re-run the same test.
Then fit a BEM (and / or try the Vector super unit) and re test to see what reduction in consumption they may offer if any.