Boiler losing pressure overnight

Question

so, i have an ideal logic combi boiler which although working seemingly well , the pressure drops to almost 0 when not use, mainly overnight. I do not need to re-pressurise the system as when i turn on the heating it raises to around 1.3 on its own and around 1 or just below if calling for hot water.

All radiators are full and all but one are fine apart from a cooler spot to the bottom of a bedroom one, no visible leaks.

we have two small boxes in a upstairs cupboard,with little levers on that slide from one side to the other joined to a pipe that disappears behind the void.

The box/pipe that we believe to operate the upstairs heating makes a disturbing rattling sound for upto a minute when coming on, it scared me a bit so had a BG call out under our plan and he was very dismissive saying dont worry about anything in there its just airlock, fiddled with the nearest (bathroom) radiator and left.

this has been the case for upto 6 months now, the rattling does eventually stop on its own accord or if i set the thermostat to 2/3 degrees lower upstairs the rattle doesnt occur.

Apologise if i seem to have gone way off track here, but is it worth me getting them back for a second opinion, could my boiler be an accident/expense waiting to happen or is it a case of all heating and water is working fine so dont worry about it?

thank you in advance

Answer 1

Low Pressure

It is normal for the boiler pressure to rise when the internal water is hot and fall when it cools. However a pressure close to 0 is a concern.

https://www.britishgas.co.uk/home-services/boilers-and-heating/guides/boiler-pressure.html

Topping up the boiler is fairly easy. There are many online guides and videos showing you how. Check your boiler's manual to find the correct filling pressure. This should be measured when the boiler and radiators are cold.

If you keep having to top up the boiler to maintain the cold pressure, then it is likely you have a leak or water is being lost through the pressure relief. Repeated topping up will dilute your corrosion inhibitor and it will become less effective.

Bleeding air off either manually or through an auto vent can also reduce the pressure. This is common after a major refill, but will reduce over time.

If the cold pressure is correct and the hot pressure is too high then the expansion vessel might be faulty.

A faulty pressure gauge could also give incorrect readings.

Rattling Boxes

Without a photo, I don't know for sure what these boxes are, but they might be zone control valves that switch your downstairs/upstairs radiator circuits on/off.

Normally they are pretty quiet. Perhaps you have some air bubbles trapped in the circulating flow. These can cause noises when passing through tight spots like a pump or a valve. This might sound like a light fizzing or a kind of tapping noise.

If you are concerned then get a second opinion from another professional.

Answer 2

You have air trapped in your piping system. It may not be a problem right now, but usually water heating systems are less effective when air is trapped and you may lose heating power or even damage the system.

Most radiators come with a valve to release air that you have to open long enough until water drips out. Start with the radiators in the upper floors. Once the trapped air is gone, make sure there are no leaks anywhere that could allow air back in. If you have a leak and can't find it by yourself you may have to hire a professional.

Here is a video showing how to do use the radiator air valve: youtube