Thank you for your reply. We’ve just had an engineer come out. We got the engineer to come out because 2 morning’s ago, after the boiler had been off overnight, it did not come on again in the morning, because the pressure was too low. I re-pressurised the boiler until the pressure gauge read between 1 and 2 and the boiler then came on, but shortly afterwards water started coming out continuously from the pressure relief valve outlet pipe. I looked at the pressure gauge and it was reading well into the red, beyond 3. After a few minutes, water stopped coming out of the outlet pipe, but the pressure gauge was still reading beyond 3. As the pressure was not going down and the temperature was still rising I opened one of the radiator bleed valves to let out some water from a radiator in order to reduce the pressure. I let out about 400 millilitres and the pressure gauge dropped to just under 2, so I closed the radiator bleed valve. The boiler then worked okay and the pressure gauge went down to mid-way between 1 and 2. The boiler worked okay for a few hours providing heating and hot water but later in the day it stopped working and when I looked at the pressure gauge the pressure was reading below 1 and the boiler would not come on again when I tried to reset it. I did not re-pressurise the boiler because it seemed to me that it should not need re-pressuring again with a few hours of having been re-pressurised and so there must be a fault, so I called an engineer out. Neither I nor the engineer could find any visible leaks. He pumped air into the expansion vessel. He also drained water out of the magnabooster, which came out clear. He drained approx. 2 to 3 litres of water through the magnabooster and put in 2 tubes of Fernox F4 into a ladder towel radiator. Also, he removed the pressure relief valve, inspected it and put it back on again. We don’t think that there was a slow drip from the pressure relief valve outlet pipe before his visit, but we’ve now got one. Since his visit a drip forms and falls about once a minute from the pressure relief valve outlet pipe. Is this drip likely to stop after a day or so, or is it likely to continue and possibly get worse and if so, should we call him back now? I’d be grateful for any advice.
Also, as he drained between 2 to 3 litres of water via the magnabooster, should he have replenished the inhibitor in the system or is the loss of inhibitor insignificant when around 3 litres of water is drained from the system? (He told us that the F4 that he put in the system also acts as an inhibitor but after looking it up on the Internet it doesn't look like F4 does act as an inhibitor.)