Adjusting Pressure On My Potterton Gas Boiler- Help Please!

[moggie 939]

The pressure keeps falling on my boiler every few months (it has been serviced regularly) and the gauge needle foes into the low green and it switches off. Under the boiler there is a 'loop' with two taps which the engineer told me to open slightly until the needle goes up into the top of the green area.

There are two levers one for hot and one for cold water I suspect. I think I may have only opened one as it wen very high into green and although the boiler worked when I got up next morning it had gone back to low green and would not start! So I opened BOTH taps just a little and it seems ok now. Did I do right?


Thanks everyone


Moggie

[New Judge]

The two levers are both to isolate the boiler from the (cold) mains supply. To top up the system you should firstly open the one nearest the boiler fully. Then you should open the one furthest from the boiler slightly and observe your pressure needle going up. When it has reached the required level, reverse the process making sure both taps are fully off.

Pressurised systems tend to lose pressure gradually over time Dissolved air comes out of the water and gathers in the system. Hence the need for an occasional top-up. At the same time you should ensure your radiators are bled of air (it will usually gather at the highest point in the system).

[Mamyalynne]

This video may guide you in how to operate the taps etc.

[Mamyalynne]

Cross posted with NJ there , sorry.

[Atheist]

I presume that there is a short flexible loop with a valve at each end. When both valves are opened, cold water (not hot) can enter the heating system (not the tapwater system) and the pressure will rise until you close both valves. Strictly speaking you should then remove the loop, but it's not worth the trouble. When the water in the heating system gets hot the water expands and this expansion is taken up in an expansion vessel. The expansion vessel contains heating system water and air, with a flexible membrane to separate the two. When the water expands into the vessel, the air is compressed and the pressure shown on the pressure gauge will rise. The air in the vessel can be topped up using a car tyre pump - if there is insufficient air then there is nowhere for the expanded water to expand and the pressure will rise until the pressure release valve opens at 3 bars to release excess water, in the interest of safety. It may be that the expansion vessel needs topping up with air, or it may be that the vessel needs to be replaced because of a leak which results in loss of air pressure. An engineer would be needed in either case, unless you are capable of locating the vessel's air valve and topping up the air yourself. Good luck.

[moggie 939]

Thank you everyone - understand now and have taken the action and all seems ok - boiler is 8 yrs old and has been working perfectly and is serviced every year
moggie