Weeks ago I floated, for amusement only, the notion of using my existing Thorn multipoint gas water heater to power a new central heating system (with a thermal store). Well, I spent half the summer putting it all in and I'm now testing with the multipoint hooked up (yes really!). I've incorporated much of the hopefully excellent advice from Dr Evil and other folks along the way.
The result?. Well it basically works... almost!. The boiler fires up when it's supposed to and gets the 180L store 'hot' in about 15 mins or so. But I have one problem, boiler 'kettling' (water audibly sizzling / simmering from boiler, which also gets rather hot - albeit it's high summer).
Rough measurements suggest the boiler is processing about 10L/min, and raising the temp by about 30C in one pass. The flow is just like it used to be, but obviously the water-in is warmer than cold mains. The bolier's h ex is some galvanised enclosure containing wrapped 15mm pipes, so is perhaps low water content. I have an open system with the FE tank in the loft and pumps/thermal store on the ground floor, with boiler on 1st floor. The primary pump is a Wilo gold 60 running at top speed (adifferent pump delivers to the radiators). The boiler pipe run is unfortnately (but unavoidably) long, about 12m each way in 3m vertical, 28/22mm pipe, with about a dozen 90 degr bends.
I'm thinking that water needs to be be run through the boiler more quickly, say 30L/min, reducing the temperature differential to about 10C. This purely to quell the kettling. I wanted to ask:
1) What is the typical flow rate through a CH boiler - is it usually more than 10L/min and2) For whatever reason the Wilo docs suggest a much higher flow (3-4m3/hr =
45-66L/hr) than I'm actually seeing. Assuming the Wilo isn't crocked, or blocked, and I need to increase flow by about 3x, can anyone suggest a suitable new pump?.The other things I can think to try are raising the FE tank in the loft (by about 1.5M), try to de-scale the exchanger (previous attempts seemingly unsuccessful - BTW who exactly would sell a suitable replacement?)) or add stuff to the water, which will be expensive (esp gel silencer) because of the large volume of water in the direct store. Or (Heaven forbid!) get a new boiler put in...
Egremont.
PS - will I getaway with leaving it a few weeks before putting corrosion inhibitor in?