Slight pressure drop.

[dingdangdo]

Hi. I have a boiler which is approx ten years old. A few months ago we had the expansion vessel replaced by a BG plan but noticed that there was a slight pressure drop since they fitted it. The copper pipe outside had an odd drip here and there. On top of that I had to have a valve on one of the rads replaced as this was leaking. The whole system was dropped so this could take place. No leaks anywhere else around the rest of the rads. Since the system was dropped the PRV no longer leaks but I'm still getting a slight drop in pressure probably 0.1bar over a month. I noticed that when the weather was warmer the pressure more or less has stayed the same but since the cold snap ie minus temp the pressure has dropped slightly by just less than 0.1bar. Hardly owt. My question is is can pressure on a boiler fluctuate when there has been no heating on for a day ie system is cold. So the colder the pipes get can this alter the pressure on the Guage slightly? Only other thing to add is when the pressure is set at 1.3 and the heating is on the pressure goes to approx 2.6 / 2.7 but doesn't go over three and looks like nothing is being dumped out of the copper pipe outside.

 

[cjg]

what size are the rads, how many, did he put the right size expantion in?

 

[dingdangdo]

There are 11 rads in the property and the expansion vessel that BG changed was just a straight swap with the old one. The eleven rads include two towel rads, a small rad in the downstairs loo, one in the hallway, two in the kitchen diner, one in the living room and then just three in the bedrooms. Size wise...I'm struggling with. I know that the kitchen and the living room ones are doubles if you understand non diyers like me

 

[John.g]

"Only other thing to add is when the pressure is set at 1.3 and the heating is on the pressure goes to approx 2.6 / 2.7 but doesn't go over three and looks like nothing is being dumped out of the copper pipe outside."

2.7/2.8 bar should be the max, 3bar is too much as the PRV will/should lift at that pressure and thats why it doesn't go over 3.
Was this a external E.vessel?, if internal what is the make/output of your boiler?.
Even a 8L E.vessel with precgarge & filling pressures of 1.0/1.3should deal with 100 Litres of system water without exceeding 2.12bar and 144 litres withoutbar exceeding 2.7bar, doubt if your system is larger than 100/120 Litres at most.

 

[dingdangdo]

"Only other thing to add is when the pressure is set at 1.3 and the heating is on the pressure goes to approx 2.6 / 2.7 but doesn't go over three and looks like nothing is being dumped out of the copper pipe outside."

2.7/2.8 bar should be the max, 3bar is too much as the PRV will/should lift at that pressure and thats why it doesn't go over 3.
Was this a external E.vessel?, if internal what is the make/output of your boiler?.
Even a 8L E.vessel with precgarge & filling pressures of 1.0/1.3should deal with 100 Litres of system water without exceeding 2.12bar and 144 litres withoutbar exceeding 2.7bar, doubt if your system is larger than 100/120 Litres at most.

The boiler is a baxi 35c exclusive. Reading the manual it says its fitted as standard an eight litre EV

 

[John.g]

As long as the pressure doesn't exceed 2.7/2.8 bar then OK but if its hitting 3.0bar then BG should recheck the precharge and filling pressures and if OK then possibly requires a external E.vessel.
Any idea what the max pressure was previously?

There shouldn't be as much as a drop of water from the PRV, if they do return get them to renew taht as well.

 

[dingdangdo]

As long as the pressure doesn't exceed 2.7/2.8 bar then OK but if its hitting 3.0bar then BG should recheck the precharge and filling pressures and if OK then possibly requires a external E.vessel.
Any idea what the max pressure was previously?

There shouldn't be as much as a drop of water from the PRV, if they do return get them to renew taht as well.

It's only ever hit over 3 bar a few years ago. The reason why BG had to fit a new EV was due to them damaging the original one when all they were doing was replacing Schrader valve. Once they fitted it the PVR started to leak a little into the copper pipe. That stopped ish when another plumber replaced a valve on the rad cos they had to drain the whole system. From my original post can the pressure drop a tiny bit ie 0.1 bar due to the pipes in the house being colder than normal temperatures with the recent freeze on temps. I'm getting obsessed with looking to see what the pressure is reading on these boilers. I've noticed the Guage reading just below 1.4b and then the next morning when the temp been in the minuses outside it can drop to 1.3b.

 

[John.g]

The drop in pressure can be accounted for if the whole system contents temperature fell by ~ 7C from the night reading. But of course if you read the pressure when the boiler shuts down overnight it might be say 2.2bar and when the contents cool overnight the pressure may be down to 1.3bar depending on system temperature.
IF the system temperature fell to exactly the same temperature when BG filled the system to 1.3bar then barring no leaks, it will fall to exactly 1.3bar.