Dripping outside pipe cowl vent
Water is dripping from the pipe cowl vent which is situated on an outside wall. We have a pressure water system and the hot water and central heating is provided by an outside boiler. It is not a combi-boiler. We have two pressure units on the system. One white and the other red. Does the pressure in one or other (or both) of these need checking. Might that solve the problem? Thank you for your help.
Advice from 1 local tradesperson
Yes, the dripping from the pipe cowl vent could be related to the pressure in your system, particularly if you have an unvented (pressurized) hot water system. Since you mentioned having two pressure vessels (a white and a red one), here’s what they likely are and how they might be connected to the issue:
Understanding the Two Pressure Vessels:
Red Expansion Vessel – Typically for the central heating system. It absorbs expansion when the water heats up.
White Expansion Vessel – Usually linked to an unvented hot water cylinder. It helps manage water expansion in the hot water system.
Possible Causes of the Dripping & Fixes:
Over-Pressurization of the System
If the expansion vessels have lost their air charge or are faulty, pressure can rise too high when the water heats up, causing the pressure relief valve (PRV) to discharge excess water through the external pipe (which might be the pipe with the cowl vent).
Fix: Check the system pressure on your boiler’s gauge. If it’s too high (above 3 bar for heating or excessive for hot water), the expansion vessels might need recharging or replacing.
Faulty Pressure Relief Valve (PRV)
If the PRV is faulty or stuck open, water will constantly drip from the discharge pipe.
Fix: A plumber may need to check and possibly replace the PRV.
Air or Waterlogged Expansion Vessel
Over time, expansion vessels can lose their air charge. If the vessel is full of water (instead of air), it won’t function properly, causing pressure fluctuations and water discharge.
Fix: The expansion vessel’s air pressure should be checked using a pump and gauge. If low, it needs repressurizing (usually to around 0.9-1.5 bar, depending on the system).
Excessive System Pressure from Overfilling
If too much water has been added to the system after maintenance, it could cause overpressure and trigger the PRV.
Fix: If the heating system is over-pressurized, you might need to bleed some water from a radiator to bring the pressure back to normal.
