I've been going around in circles with this problem.
I have a Protherm 80e Combi Boiler with the following problems which I don't know if they are related or not.
1: When the heating is switched on the boiler ignites ok, heats up until I get a reading of 42 on the display and then cuts out. It then comes back on automatically when the reading hits 28 and so on... The result of this is that none of the 7 rads get very warm so it's not worth keeping the heating on. Sometimes I get an error message saying FO which according to the manual means
Flow rate sensor failure, loss of system water, air lock in boiler or pump failure.
I have checked the pump is spinning by looking that the end of the spindle after removing the bleed screw. Looks ok. Is it possible it could sill be damaged and need replacing.
2: Although I had heating problems the hot water worked fine until two weeks ago. Now it goes hot and cold. To get it working I have to turn on the heating to get the pump running, then turn on the hot tap and eventually the boiler will ignite. Sometimes the water will stay hot, others it goes hot and cold.
I've had a corgi engineer out from e-On. He didn't fill me with much confidence. He had to call the manufacturer, gave them various readings which he took using various meters. Apparently these seemed ok.
He thought it could be the Pump, Diverter Valve or Flow Rate Senor causing the problem but wasn't sure if it would work even if he replaced all these. He looked puzzeled by the boiler and relyed a lot on the manual. In the end he just said what the manual said might be wrong. He said he would order the part's but never got back to me.
My question is could I need a new pump if I can see the one I have is spinning. Also would this be the likely cause of the boiler cutting out when it reaches a certain temperature.
Things I have done to date.
Replaced the Thermistor, cleaned the heat exchanger, flushed all the rads using a cleaner and water via the filling loop?
I've changed what the user manual refers to as the CH Temperature Sensor on one page and Thermistor on another. I noticed one of the electrical connections was lose on it.
I haven't replaced the DHW thermistor
I haven't replaced the overheat thermostat / high limit thermostat.
I have taken the pump apart. The impeller was stuck but I managed to free it up. When doing it I heard a pop sound. Seems to be turning freely now although I did notice a little resistance on and off. When running it does make strange sounds like it's now and again. Other times it hums very quite.
When I can get the CH running the heating flow pipe between the heat exchanger and pump does get hot but as you say the pipes a few meters away are only slightly warm at best
This is probably a stupid question but does the DHW rely on the pump or could this be an unrelated problem??