3 mm pebbles are quite relatively heavy and not that easily made to move up a vertical pipe with typical flow rates.
My original comment is that it probably still was dropped into the pipe during the installation.
Although the boiler does not have a mesh filter it does have a flow limiter which has a very small orifice and would normally block anything as big as 3mm. Sometimes the flow limiter is removed to improve flow rate by the installer.
Many of the "Y" strainers actually have a coarse and a fine mesh on top of each other. The fine mesh can be peeled away to leave the coarse one if yours is that type.
They should also be installled contrary to the arrow on the casing so that the filter is pointing down so when they are opened the dirt falls out rather than just back down the vertical pipe.
Tony
My original comment is that it probably still was dropped into the pipe during the installation.
Although the boiler does not have a mesh filter it does have a flow limiter which has a very small orifice and would normally block anything as big as 3mm. Sometimes the flow limiter is removed to improve flow rate by the installer.
Many of the "Y" strainers actually have a coarse and a fine mesh on top of each other. The fine mesh can be peeled away to leave the coarse one if yours is that type.
They should also be installled contrary to the arrow on the casing so that the filter is pointing down so when they are opened the dirt falls out rather than just back down the vertical pipe.
Tony
