I have a Glow Worm Ultracom 18HXi boiler which has a problem controlling the outlet temperature, as it cycles about every 20 to 30 seconds, plus/minus 2 degrees. This variation gets worse until the boiler trips out on over temperature. It then restarts and does the same thing once it reaches the set point of 70C. The boiler manufacturers say it is a system problem. The boiler is 6 years old and this problem has been occurring for about 2 years, but is getting worse now. The system itself is 30 years old. On commissioning the temperature rise across the boiler was 17 C on full fire, but now it is about 21C on full fire. The manufacturers state that the maximum temperature rise should be 20C. Any ideas?
