Hi we have an Isar boiler HE30 i think the model is. The pessure has dropped to the lowest on the valve and is making a noises like it is trying to heat up but is not managining to and is worrying me, would it be a problem to leave this on overnight, would there be any problems? I have put in some more pressure earlier to between 1-2 on the valve but this slowly reduced over a period of an hour or so back to the bottom, making me think there is a leak. Could i please get some advice on this??

liam clarke, February 2012

Hi Liam,
If you go outside to the wall that the boiler terminates out of you will usually find a 15mm copper pipe sticking out the wall about 3/4 feet below the flue. This pipe may either curl back against the wall or just hang a little way or run all the way to the ground. Whichever way it goes, stick your finger over the end and feel if there is water coming out of it. If there is then your Pressure Relief Valve (PRV) is letting by. Now this will either be because someone has worked on your oiler and used the PRV to let water out and it hasnt resealed properly or the more likely cause is that your system has over pressurised and the valve has done its job and opened at 3bar. Now the reason is has over pressurised is normally because a part in teh boiler called the expansion vessel has perished internally. What this vessel does is allow for expansion in the system. When you heat up water it expands and if you heat up water inside metal with nowhere to go it will explode, so they put in an expansion vessel which compresses air as the water expands and allows for safe use of a sealed system. Then incase this goes wrong they put a PRV in to jettison all water if the system exceeds 3bar. Now if this is hte case you will need to get a gas safe engineer in to repair your system. It is safe to use as it will cut out on its stats if it gets to hot, just keep an eye on the pressure and set it to 1.5bar before you go to bed to make sure it sees you through the night. If you are practical and confident you can drain half of the water out of one of your radiators and leave it so its hot at the bottom and cold on the top during operation. This air bubble in the rad will work as a temp exp vessel but it is not a long term solution

Martin, February 2012