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Brown Oily Residue Blocking Air Vent and Weeping Relief Valve... Anyone Seen This?

seoras · 2026-05-06T08:55:33Z

My installation is 4 years old. After about 18 months a brown coloured leak appeared around the press/temp relief valve on the DHW cylinder. It’s still unexplained. In any case, I considered the valve would need to be replaced or reseated. In case the leak worsened, I wanted to know how this valve was sealed to the cylinder protruding boss that accommodated the valve – was it a parallel or taper pipe thread? How was it sealed? Or was it a design that incorporated mating faces sealed with an O-ring? No rational response and notable exasperation that I should ask such questions – presumably because they didn’t know. I was trying to be prepared in case I had to suddenly deal with it. Last week, I experienced a leaking air vent on top of the buffer cylinder. I asked if they had a part number. The number I was given was a purge/bleed screw, which looked like a small screw with a hole to allow air escape when loosened. I now realise the air vent was added by the installers but it fitted into a ½” boss, not something that would accommodate a bleed/purge screw. Other instances around guarantee registration (website registration on the card didn’t exist/German address on the card) were met with indifference. I compare this with very positive help from Worcester Bosch over ten years, including guiding me in sorting plumber’s bodged repairs. For the brown gunge leak, they suggested limescale. It still beats me why that should emanate from around that valve. Similarly, the leaking air vent was, on examination, due to an accumulation of brown oily gunge blocking its exhaust. Any suggestions as to what it is are most welcome.

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Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls

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Fred Gray

(@fred-gray)

New Member Member

Joined: 9 months ago

Posts: 2

10/05/2026 1:40 pm

In London we have a free hazardous waste collection service. I assume all areas have the equivalent.

https://www.cityoflondon.gov.uk/services/waste-and-recycling/hazardous-waste-collection

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4577

10/05/2026 1:40 pm

@seoras that's genuinely frustrating, and you're not alone in that experience. The disposal infrastructure for glycol from domestic heating systems is woeful... it's one of those areas where the industry has pushed a product into hundreds of thousands of homes without thinking through the end-of-life problem. You're left holding it, literally.

Very similar to end of life heat pumps that can't get scrapped until refrigerant is recovered.

On the wider point... you're right to be annoyed. Glycol in residential heat pump systems is often specified as a default when it isn't actually necessary. If the system is designed correctly with adequate freeze protection through flow management and controls, many installations simply don't need it.

I'll make some enquiries tomorrow with my installer network.

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