low water pressure in Ferroli Maxima 35S

[pequay]

I have an 8 year old Ferroli Maxima 35S boiler which regularly loses water pressure. When hot the water pressure reads around 3 but as soon as it gets cold it drops to less than 1 and after a day or two it needs pumping back up. There are no obvious signs of a leak and I had the pressure relief valve replaced a couple of weeks ago. That seems to be working OK now. Before I start digging up the pipes under the floor to see if there's any leaks is there anything else I can do?

 

[ianmcd]

your pressure should only be between 1 - 1.5 bar when cold , it will rise slightly when hot but should never go as high as 3 bar, your pressure releif valve is designed to open at 3 Bar so that is probably where your water is going

 

[pequay]

Hi Ian,

Thanks for the reply. I had thought the big difference in pressure between hot and cold was a problem. What can I do about it? I have read that the low pressure sensor might be a problem. Is there any point in replacing it?

 

[ianmcd]

the low pressure sensor usually operates about 0.2 bar some I think may be 0.4 Bar its easy enough to test the low water contents switch on your boiler it is just a simple make and break switch so if you have a multimeter turn the power off and see if you have continuity through the switch, if when you set the boiler pressure to between 1 - 1.5 Bar cold and the pressure rises when hot to 3 Bar then that is an expansion vessel problem

 

[pequay]

Does that mean I have to get the expansion vessel replaced? If so how much is that likely to cost?