We have a Heatline C28 HE Condensing Combi Gas Boiler, we use the boiler to heat water for shower and dishes mainly, and from time to time for the heaters in the rooms. Until yesterday the behaviour of the boiler was quite normal. But yesterday evening we turned on the boiler to the winter mode, to heat the heaters in some rooms of the house. We moved the central heating temperature controller to the maximum position and the boiler was working the whole night perfectly. But this morning one of us had a shower and was working well, but a little bit later I tried to have a shower and the boiler was not heating. We went to check out the control panel and the led corresponding to "check overheat safety thermostat" was flashing. We turned off the boiler to summer mode and the led stopped flashing. We tried to heat a tap water and was not working. The boiler made a noise like when is going to start working but nothing happened. We tried several times leaving the boiler for a while to let it chill. But it was not working. Sometimes it started to heat, we could see the heaters inside the boiler burning, but in 10 seconds more or less the pressure indicator started to go up from 1.5 (normal position) until 2.5. When it arrives at that point the boiler does a really weird noise and the pressure goes down and the heaters inside the boiler turned off. As soon that thing happens we close the tap water because we do not want to know what could happens after. so, there is the problem, I hope you can understand what we mean. It could be really good if somebody can give us an idea or solution about what is going on. Thank you very much for your time and attention. Kind Regards.