Hi we have a Keston 170 and have had a few problems with it over the past 7 years, but now there seems to be a "cycling" problem. The bioler will fire up, run for about 33 seconds, wind down, shut off for about 33 seconds and fire up again. Electric bills and gas bills have gone up considerably. Keston say could be any number of problems. have had a new heat exchanger fitted and various thermostatic switches in case they were sticking on. Still runs in its cycle of twice a minute. Any help would be good. Thanks