open fire back boiler problem

[danhar707]

We have an oil fired boiler on a c-plan arrangement with a 7day 2ch programmer. i.e pumped ch and gravity fed ch with a 2 port valve controlled by a cyl thermostat. Tank was moved into he attic by our plumber when we moved in 2yrs ago (so we could have an extra cupboard upstairs.) shortly after moving in, we found out in an eventful way one night that there was a back boiler... we had a raging fire going in the living room and heard gurgling noises and then sound of water pouring onto the conservatory roof.... so i guess the back boiler works! i called he previous owner who built the house and he claimed to have no knowledge of a backboiler being installed. hmmmm.

ive got a couple of problems im hoping to get some expert input on....
1. I can heat the cylinder until the valve closes on an evening and valve is still closed at 6am; then the boiler is set to fire at about 6.30 until 7. without fail, the valve is open again by 7 (call for heat light on). its as if firing the boiler and pumping for the ch is sucking heat out of the tank. when i canceled the moning heating, the call for heat didnt come till early afternoon and i was even freezing outside. i think theres a 10degc hysteresis on the cyl t stat, so quite happy that the tank is holding heat ok.

2. ive noticed that whenever the boiler is on for dhw, a vertical area on the right hand side of the chimney brest feels warm to the touch. seems to me that the hot water is circulating up and then back down round the back boiler. im guessing this is very inefficient, with lots of heat going up the chimney that should be going into the dhw tank! wondering if anything can be done to stop or reduce this. reluctant to loose the back boiler facility as we do have a fire half the nights in the winter. any ideas?