I have a Worcester Bosch Greenstar 24ri gas fired boiler for water and central heating. Hot water is via an indirect cylinder, tank stat set to 60C and boiler set to give flow temperature at around 73C (measured using contact thermocouple on pipe). Grundfoss pump set on speed setting 2 of 2. Time clock is set for a 1 hour cycle in the morning.
Problem: At the start of the cycle the boiler fires and runs for around 35 minutes. Boiler then stops firing but zone valve is still open and pump running because tank not up to temperature. Flow temperature drops to around 57C but boiler does not re-fire for 15 -20 minutes. System shuts down at the end of the one hour cycle. If I let it run beyond the one hour the boiler will re-fire eventually and the tank will get to temperature in about 90 minutes.
I first noticed this problem when the boiler was installed 3 years ago. The installer just increased the boiler thermostat setting but, because of the layering effect in the tank, the hot water was scalding. I persuaded Worcester Bosch to investigate in 2022 but the engineer said that the boiler was firing correctly (i.e. it went up to temperature) and did nothing. I have had another WB engineer to look at the issue this week and he observed a 20C drop in flow temperature before the boiler re-ignited. He changed the main circuit board (but did not change the temperature sensor) and said that had solved the problem but he didn't wait to check! (Was in a rush to catch a bus!!!) Nothing has changed and the system is still behaving as before.
WB has said that if the problem persists I will have to have the whole system flushed. The installer insists that the system was flushed during installation and that the problem must be with the boiler. I am stuck in the middle!!
Any ideas would be welcome please.
Problem: At the start of the cycle the boiler fires and runs for around 35 minutes. Boiler then stops firing but zone valve is still open and pump running because tank not up to temperature. Flow temperature drops to around 57C but boiler does not re-fire for 15 -20 minutes. System shuts down at the end of the one hour cycle. If I let it run beyond the one hour the boiler will re-fire eventually and the tank will get to temperature in about 90 minutes.
I first noticed this problem when the boiler was installed 3 years ago. The installer just increased the boiler thermostat setting but, because of the layering effect in the tank, the hot water was scalding. I persuaded Worcester Bosch to investigate in 2022 but the engineer said that the boiler was firing correctly (i.e. it went up to temperature) and did nothing. I have had another WB engineer to look at the issue this week and he observed a 20C drop in flow temperature before the boiler re-ignited. He changed the main circuit board (but did not change the temperature sensor) and said that had solved the problem but he didn't wait to check! (Was in a rush to catch a bus!!!) Nothing has changed and the system is still behaving as before.
WB has said that if the problem persists I will have to have the whole system flushed. The installer insists that the system was flushed during installation and that the problem must be with the boiler. I am stuck in the middle!!
Any ideas would be welcome please.
