I then just refilled the boiler, vented it and tested the system. It?s a nice easy job that shouldn?t take more than an hour. What Else Can Cause This Problem? Split Expansion Vessel If your Vaillant boiler is losing pressure overnight you will have a leak somewhere on your heating system or the pressure relief valve is letting the water out. You should ensure the heating is turned off before repressurising the boiler as it will sometimes fire up as soon as it reaches the minimum working pressure.

Having been reading various threads here and from watching the boiler this morning I think I have gotten close to the problem. Another cause could be the expansion vessel has lost its air and needs to be recharged or replaced.

vaillant turbomax - expansion vessel + valve

The system pressure kept going really high when the heating was on. But when the heating cooled down, the pressure went really low and caused an F22 fault. What Causes Boiler Pressure To Go Really High

This means the expansion vessel on the Vaillant boiler might not be big enough and can cause problems with the pressure.If you need to repressurise your Vaillant boiler often you have a problem that you need to get fixed. Recognised Grundfos high-efficiency pump - Modulating high-torque pump uses low energy to deliver a balanced output to meet the boiler demand, helping to reduce energy consumption This is usually below the boiler but there could be an external flexible filling loop anywhere on the system, sometimes hidden away in cupboards or behind boxing. Vaillant boilers are sometimes undersized when fitted and are not large enough to cope with a large house’s central heating system.

The pressure rises when the heating is on, so you will not get the proper reading until it has cooled down. If the pressure drops, it means the water is getting out which should not be happening. Low pressure on a Vaillant boiler This is most likely an expansion vessel problem, if so, you will need to recharge it or replace the expansion vessel if the diaphragm inside is split. I'm no expert at all but from reading lots it points to the expansion vessel either needing a recharge or is failing/failed. I see that you can test the Schrader value for water. I also read that vessels last around 10 years, which if true means we're fairly close to it. Removable side panels and push-fit flue system - For improved accessibility and ease of installationOther causes of the pressure going too high on a Vaillant Ecotec are the boiler?s built in filling loop letting by. This is the part of the boiler that lets you top up the system pressure if it goes down. Sometimes these valves don?t close properly and keep letting water in the boiler. Getting the best combi boiler for a large house is very important, but adding an external expansion vessel that is large enough for the central heating system is also an option rather than upgrading to a bigger boiler. External expansion vessel fitted

Controls compatibility - The wide range of Vaillant room thermostats, wired and wireless controls including the vSMART™ app-based control with weather compensation to lower running costs for tenants What I have learned and understand so far is that there should be a release of air from the valve when activated when the boiler is switched on or off. You might bet a Vaillant F83 fault code on some boilers when the pressure is too low. Expansion Vessel ProblemsThank you so much everyone for your responses. I've read through the FAQ and it makes sense on the whole. I just have a couple of questions: The most common cause of a Vaillant boiler losing pressure is a leak, this could be on the boiler or anywhere on the central heating system. Having the boiler pressure too high (above 1.5 when the system is cold), means you will need to let some pressure (water) out of the system. However if the system is under pressure then my understanding is that of course water would come out of the air valve and the person doing the job is trying to con me into getting unnecessary work?