Leaving mains valve into boiler system open

blue_steel

Hi, any opinions on the following would be appreciated.
We had a new condensing boiler installed about 8 months ago.
After all the work was complete and almost as an after-thought the guy who installed it told us we had insufficient water pressure for the system.
It requires 1.0 bar to operate and there was only a pressure of 0.8 bar in the mains. He boosted the pressure up within the system using a hand-pump and it worked great for about 4 months. Then the pressure in the system dropped below 1 bar and it cut out. We were getting work done on the kitchen at the time and that may have caused the drop in pressure so I just called the guy out and he pumped it up again.
After this I decided to keep a close eye on the pressure. It started off (in Sept) at 1.8 bar. I have checked it periodically since and at one stage it was down to 1.0 bar. If the heat is on all day it seems to go back up a little (currently 1.3) but the trend is obviously downward.
I have had the council out and they measured the pressure entering the house at 2.0 bar so the loss of pressure is obviously internal. I could have got a plumber to see if he could find the problem but seeing as the boiler was under warranty and is not operating as it’s supposed to I decided to get the installer back.
Anyway to cut a long story short he has now suggested leaving the mains valve into the boiler system open all the time so that when (if?) the mains pressure goes up during off peak times it will boost the system. Is this a good idea? Something about just leaving the mains valve open doesn't sound like a good idea to me.
Thanks in advance and sorry for the longwinded question.

Joey the lips

No this cannot be done. Your introducing new oxygenated water to the system all the time this will cause the system to prematurly age corroding the rads and causing a leak a lot early. If pressure is dropping its because it is escaping somewhere in a sealed system this is wrong.

Now if he wants to leave the mains connected to the boiler where this is a combination boiler as in instant hot water this is fine. but I suspect this is not the case.

You're problem is not a warranty issue as the manufactures will tell you not to fit their boiler without enough pressure on the incoming mains, all sealed systems leak microscopically and it's not unusual to have to top up the system a couple of times a year, so the problem will not go away, if you have 2 bar coming in the property then you should have 2 bar at the boiler as the pressure will equalize after a time. You may have to look at converting to a tank fed system if you're boiler is compatible, ask the manufactures direct if it can be done, agreeing with Joey you are in danger at sludging up your new boiler , if you have inhibitor in the water it's less of a issue and you would have to top up the concentration of the inhibitor, if not think about flushing and adding a inhibitor Gary.

blue_steel

Thanks lads.
He has said we will need to add an inhibitor once a year when we get the boiler serviced. But I agree that it is asking for trouble adding fresh water to the system on a constant basis.
I think I will get a plumber in the new year to try and solve the low water pressure problem. If I could fix that then the boiler would follow.
The pressure is dropping somewhere between the mains supply and the drinking water tap (as least I think so because that tap pressure isn't great). I'm hopping its something simple like the gate valve under the sink needing to be replaced. It is pretty old. I've oiled and opened it as far as I can but it hasn't had any effect. There could always be a underground leak I suppose but fingers crossed its not that.

The gate valve would stop flow not pressure as the pressure would equalize after you turned the tap off, when you opened it again you would get a initial blast of the 2bar which would be your standing pressure and it would drop down to the working pressure which can be lower, the only things that would stop the pressure on the boiler reaching the 2 bar they are telling you you have would be a pressure reducing valve fitted somewhere, a leak, they are lying, or defective filling loop, because the heating system is a closed system the pressure should (without sounding like a stuck record) equalize, Gary.

blue_steel

What is meant by equalise? If the boiler system is closed and it is reducing will it not just keep reducing unless it is topped up by opening the mains valve?

You have water pumped in at 2bar as it enters you're property, you're standing pressure which is when everything is closed(taps etc..) Will be 2 bar, anything thats connected to the mains will be at 2bar as the pressure will keep pushing until it reaches 2bar and is equal across the pipe work once it does reach 2bar, it will have equalized across all of the mains pipe work, when you open the filling loop to fill the heating system it becomes connected to the mains pipe work and will have water pushed in to it till it matches the incoming pressure as it is a closed system, the leak would have no impact as it takes 4 months to lose the pressure in the rads, it wouldn't take that long to fill the system if you had 2 bar coming in, isolation valves/stop cocks and poorly sized pipe work will only effect flow of water and working pressure, it will not stop the standing pressure of the pipe work from reaching the same as the incoming pressure, Gary.