Expansion vessel pressure & heating system pressure

Nicolas_Bandon

Hi,

My home is a 2 storey house. I have a Grant Vortex Outdoor Condensing Oil Boiler (model 90/120). The boiler is outside and the expansion vessel is in the attic. In the manual it is said that the pressure gauge on the boiler must indicate between 0.5 and 1.0 bar when the system is cold. The highest point in my installation is the expansion vessel (static head: 6 meters) and the expansion vessel size is 18 liters.

Does anyone know what should be the boiler pressure and the expansion vessel pressure?

Are these pressures correct:1.0 bar for the boiler and 0.7 bar for the expansion vessel?

John.G

Nicolas_Bandon wrote: »

Hi,

My home is a 2 storey house. I have a Grant Vortex Outdoor Condensing Oil Boiler (model 90/120). The boiler is outside and the expansion vessel is in the attic. In the manual it is said that the pressure gauge on the boiler must indicate between 0.5 and 1.0 bar when the system is cold. The highest point in my installation is the expansion vessel (static head: 6 meters) and the expansion vessel size is 18 liters.

Does anyone know what should be the boiler pressure and the expansion vessel pressure?

Are these pressures correct:1.0 bar for the boiler and 0.7 bar for the expansion vessel?

A EV installed in the attic and assuming a prepressure reduced to 0.5 bar and a filling pressure of 1.0 bar will mean 1.6 bar (due to static head) at the boiler which is fine. If one assumes a system volume of 150 litres and a expansion vol of 3 litres, 2%, at a boiler mean temperature of 70C, this will result in a EV pressure of 1.6 bar (2.2 bar at the boiler) again fine as the boiler PRV lifts at 3.0 bar. If one assumes a system volume of 150 litres and a expansion vol of 4.5 litres, 3%, at a boiler mean temperature of 85C, this will result in a EV pressure of 2.0 bar (2.6 bar at the boiler) again fine as the boiler PRV lifts at 3.0 bar.
It would be interesting if you could give me a few pressures both hot and cold (at the EV & the boiler) and the boiler flow and return temperatures.
The above settings will ensure that the boiler will be well above the minimum of 1.0 bar.

Nicolas_Bandon

My filling loop and the pressure gauge are on the boiler. So the filling pressure and the boiler pressure are the same when the system is cold.

Moreover when the system is cold the boiler pressure must be between 0.5 and 1.0 bar and not above 1.0 bar.

John.G

Nicolas_Bandon wrote: »

My filling loop and the pressure gauge are on the boiler. So the filling pressure and the boiler pressure are the same when the system is cold.

Moreover when the system is cold the boiler pressure must be between 0.5 and 1.0 bar and not above 1.0 bar.

Thats interesting that the boiler pressure cannot exceed 1.0 bar when cold (maybe makes it easier to remove baffles etc when servicing) and also that the PRV is 2.5 bar, maybe the 2.5 bar setting is a feature of condensing boilers?.
Ideally the EV should be situated as close to the boiler as possible. Because your EV is in the attic then a filling pressure of 1.0 bar at the boiler results in a EV pressure of 0.4 bar, the filling pressure should allways be higher than the prepressure to give a water reserve so if the EV prepressure was reduced to only 0.25 bar then the water reserve would be 2.0 litres at a filling pressure of 0.4 bar. (1.0 bar at boiler)
The final boiler pressures under these conditions would then be 1.32 bar at 70c and 1.54 bar at 85C.
What is the boiler pressure when up to temperature?.

Spoke today to Grant tech. who told me that you are not limited to 1.0 bar max cold boiler pressure as long as this doesnt reach 2.5 bar (PRV setting) when hot.
My recommendations based on this info and with a 18 litre EV installed in the attic and assuming system contents of 150 litres would be:
EV prepressure 0.6 bar, filling pressure 1.5 bar (at the boiler) this gives a water reserve of 3.0 litres and a boiler pressure of 2.0 bar at 70C and a boiler pressure of 2.3 bar at 85C.
Over and out.

John.G

John.G wrote: »

Thats interesting that the boiler pressure cannot exceed 1.0 bar when cold (maybe makes it easier to remove baffles etc when servicing) and also that the PRV is 2.5 bar, maybe the 2.5 bar setting is a feature of condensing boilers?.
Ideally the EV should be situated as close to the boiler as possible. Because your EV is in the attic then a filling pressure of 1.0 bar at the boiler results in a EV pressure of 0.4 bar, the filling pressure should allways be higher than the prepressure to give a water reserve so if the EV prepressure was reduced to only 0.25 bar then the water reserve would be 2.0 litres at a filling pressure of 0.4 bar. (1.0 bar at boiler)
The final boiler pressures under these conditions would then be 1.32 bar at 70c and 1.54 bar at 85C.
What is the boiler pressure when up to temperature?.

Spoke today to Grant tech. who told me that you are not limited to 1.0 bar max cold boiler pressure as long as this doesnt reach 2.5 bar (PRV setting) when hot.
My recommendations based on this info and with a 18 litre EV installed in the attic and assuming system contents of 150 litres would be:
EV prepressure 0.6 bar, filling pressure 1.5 bar (at the boiler) this gives a water reserve of 3.0 litres and a boiler pressure of 2.0 bar at 70C and a boiler pressure of 2.3 bar at 85C.
Over and out.

More info from Grant above.

Nicolas_Bandon

John.G wrote: »

More info from Grant above.

Thanks. Now my filling pressure at the boiler is 1.0 bar and the EV pressure is 0.2 bar. No more leak! But it's strange because I never saw any trace of water at the PRV.

John.G

Nicolas_Bandon wrote: »

Thanks. Now my filling pressure at the boiler is 1.0 bar and the EV pressure is 0.2 bar. No more leak! But it's strange because I never saw any trace of water at the PRV.

Thats good news and you will now have to loose (eventually) the water reserve of over 2 litres before the boiler pressure falls to 0.8 bar. Now that there is no restriction on the maximum boiler cold pressure I would suggest that you use the higher figures (0.6/1.5 Bar) when next doing a pre pressure and filling pressure exercise.
The reason that you never saw any water at the PRV is because it never reached 2.5 bar, you possibly had 1.0 bar prepressure and 1.0 cold filling pressure initially which = not a drop of water reserve.

Nicolas_Bandon

John.G wrote: »

Thats good news and you will now have to loose (eventually) the water reserve of over 2 litres before the boiler pressure falls to 0.8 bar. Now that there is no restriction on the maximum boiler cold pressure I would suggest that you use the higher figures (0.6/1.5 Bar) when next doing a pre pressure and filling pressure exercise.
The reason that you never saw any water at the PRV is because it never reached 2.5 bar, you possibly had 1.0 bar prepressure and 1.0 cold filling pressure initially which = not a drop of water reserve.

There was a tiny leak in my heating system. So I emptied all the system (radiators & boiler) to remove the inhibitor. Then I opened all the radiator valves fully, I left the boiler drain valve open and I opened the filling loop to clean the system with fresh water. After 15min I closed the filling loop and emptied the boiler. I vigorously shaked the contents of the leak sealer bottle and put it into the boiler. Then I opened the filling loop and adjusted the boiler pressure to 1 bar. I started the boiler with all radiator valves fully open and bleeded the boiler pump and all the radiators.I kept the system operating for approximately 5 hours.
The result: no more leak!!!
The leak sealer I used is Repa-R 200. I bought it at Aquatech (Tougher, Cork). It’s expensive (€79 the bottle) but it works. Before using Repa-R 200 I used Fernox and Tec7 Plumb and Fernox F4 but they were useless!