Hi there I have an excel 80 sp which is about 12 years old , in general has been very good and has been serviced every couple of years. Diaphragm has been replaced twice along with figure 8 seals and brass nozzles. The fan was replaced 6 months ago after the slow speed resistor wire had become brittle and eventually failed. Heating and water has benn fie since but today heating has been switching off intermittently when on constant. Pressure is fine and fan is running ok. As title suggests boiler constantly fires, clicks, runs and then continues like this for a while, any one got any suggestions and also recommend someone who actually knows this boiler as last company used - CHPH - didn't seem to have a clue