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Combi boiler leaks when CH used, CH pressure gauge off scale

Postby d_cole » Sun Oct 05, 2008 10:31 pm


I have an Ideal Isar combi boiler which is approximately 4 years old. Nine months ago when it was serviced the engineer reported that the CH pressure was too high (3bar) and he reset it to 1.5bar. It soon returned to 3bar however, but has otherwise been fine all summer. Now when I turn the CH on, a leak has appeared from inside the boiler and the CH flow pressure gauge goes off the end of the scale (ie more than 4bar).
Can someone tell me what controls the CH pressure and would cause it to keep going too high? Is it likely to be a problem with the boiler or the radiator system?
Also, where would the leak be likely to be coming from?
Many thanks for your input
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Postby htg engineer » Tue Oct 07, 2008 3:29 pm

Probably pressure vessel at fault, the leak will probably be the pressure relief discharge pipe has not been tightened up - installers often overlook this when installing boiler (should be tested).

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Postby Steve the gas » Wed Oct 08, 2008 4:52 am

Is your filling loop hose disconnected when NOT in use?
This could be passing..... slowly increasing system pressure.
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Postby d_cole » Sun Oct 12, 2008 5:20 pm

Aha! There was no air in the expansion vessel. We let some pressure out of the system and used a car tyre pump to put some air into the expansion vessel, and it no longer leaks! Waiting to see if this solves it forever, or if the pressure starts to go back up again, in which case I might have a blockage in the heating system.
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