Worcester 24CDI RSF – pressure drop

[Zehroni]

Dear all
The pressure starts dropping rapidly in our Worcester 24CDI RSF boiler two weeks after I re charged the expansion vessel to 0.7 bar.
The following tests have been carried out

• Filling the system, leaving it over night no demand for DWH or CH the pressure does not drop at all.
• Checked all the pipes work under the floor broad and all the radiators connection and valves, I noticed no leak at all, and I do not there a leak in the firs floor pipe work, otherwise we would have noticed a big patch in the ceiling considering the rate it is dropping.
• Switch on the CH only for couple of hours then switch it off let the system cool down, I noticed there is not pressure drop at all.
• Checked inside the boiler including the Gas to Water Heat Exchange and found no trace of leak at all
• The drop of pressure happened when there is a demand for DHW, i.e when we take a shower for 10 minutes the pressure drops two digits i.e from 1 bar to 0.8 bar.
• This leaves me to conclude that the water to water heat exchanger is faulty. I believe some of the CH loop water is sucked in through one of the water to water heat exchanger inner pipes or walls and joins the DHW out of the system.

Is this possible or am I stretching my imagination, any help reply would be highly appreciated as this is driving me made.

 

[Nixt]

DHW exchanger internally leaking will lead to increased not decreased system pressure. When you charged vessel did you ensure the boiler drain plug left open or you're just pumping the system.

To charge vessel close F/R valves, drain from boiler point, leave it open then re-fill vessel.

 

[Zehroni]

Nixt,
Thanks for replying, I understand what you are saying indeed it increases the pressure as the mains pressure is 3 bar and the inside pressure is 1 bar. I also did leave drain plug open and there was some water coming out as I was charging the vessel . Then I refilled the system again and it was perfect for two weeks this problem start happing recently.

 

[Nixt]

Then you could check the auto air vent (top of boiler) is open and not leaking. Also the CDI has a manifold where the pressure gauge plugs in. This can get glogged and give erratic readings, if you need to drain it again check it's clean. Also check the PRV outside for drips during HW operation. (unlikely but worth a try).

 

[Zehroni]

Nixt,
Assume I did not close the F/R vales and open one of the radiators draining plug and recharged the vessel, let some water out until the pressure inside the vessel gets to 0.7 bar then close the plug and fill the system again, would make a lot of difference if I did it by isolating the boiler as you suggested.
I Also check the PRV outside for drips during HW operation, no ltrace of drop noticed.

 

[Nixt]

Don't think vessel will charge the way you suggested. When charging the vessel air pressure, the system water pressure must be zero, hence only draining boiler F/R closed.

What are you using to pressurise vessel?

 

[Zehroni]

I used normal bicycle pump with pressure gage attached to it.