The plan now is to disconnect the oil fired aga and fit a higher output wood (multi fuel) burner as a replacement to heat water and rads. There is already a heat dump rad permanently across flow and return with three zone values controlling circuits to DHW cylinder coil, bathroom towel rails, all other rads. The programmer would be redundant as the firing up of the burner is entirely manual but should the zone valves be retained with some simple manual switching maybe using the cylinder stat to give hot water priority or would it be simpler to remove those also.
Are you fitting a woodburning 'stove' (ie. something that sits inside the house and looks reasonably decorative whilst directly heating the room it's in, as well as having a back boiler) - or what you might call a 'furnace' (something whose sole purpose is to put heat into the circulating water circuit) ?
The only reason I ask, it that we've found that with our multifuel stove it's a fine balance between 'direct heat to the (big) room it's in' and 'heat to the water circuit'. You can easily have 'too much' direct heat - while trying to get the radiators heated up. Depends on the layout of your home - but the lesson seems to be that the woodburner needs to be in a big room !
Anyway - you've got the heat dump rad - so that's good. It needs to be on a gravity flow circuit - so's it will still get water if the mains / pump fails. In our case this meant siting it where I wouldn't choose to put a radiator (in a narrow hallway that backs onto the main fireplace) - but needs must !
As to controls - we neded up fitting all remaining rads (except the bathroom one) with TRVs - and this works fine. They recommend that you have a thermostatic switch on the woodburner boiler that kills the pump if the temperature drops below about 40c - something to do with corrosion of the boiler, ISTR ??
Bear in mind that the circulating water may well be cooler than you are used to (ours is generally between 50 and 60c, measured at the flow from the boiler) - this may affect the settings on your thermostats / controllers.
After much agonising , we ended up with a very simple control system - two-way valve that routes the water through the DHW cylinder if the stat on the cylinder demands it, and though the general radiator circuit at other times. So far, so good !
No doubt there are more complicated ways of doing this - but be careful of the 'sledgehammer and walnut' situation - a woodburner is a 'lo-tech' thing, very different from a oil / gas boiler , and (IMHO) doesn't require a high-tech control system.....
...but then - I'm not an expert
Good luck Adrian ======return email munged================= take out the papers and the trash to reply
Dead right.... K I S, Keep It Simple I installed a Bont ESSE Mk4 Solid Fuel room heater with a water jacket some 23 years ago. The quoted total output was 12kWatts. This stove sits in the main lounge which is 4 Metres x 5 Metres with one smallish radiator. The rest of the sytem consisting of nine radiators, one in each room. My tame Plumber told me to run two pipes as large as you can for as far as you can. This I did using 22mm pipe with 22mm to
10mm 'tees' where a radiator was needed. There is about 12 to 15 inches of 10mm pipe feeding each radiator.
This stove is alight from September through to July 24/7. I use Anthracite or to be correct Chinacite as "We" import everything these days. In the summer months I burn fallen Beech boughs, if I can find them and if it is warm enough. The pump has run for 23 years at 24/7 too. I sometimes switch the pump off to get some extra hot water. There are no TRVs, zone valves or timers. It just runs. It never gets too hot 12 miles north of Aberdeen.
I burn anthracite, mined in Wales. It's £155/tonne (Summer prices). I've used 2 1/2 tonnes so far since lighting the Rayburn in October. Anthracite is anthracite wherever it's mined.
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