Unvented Cylinder Tundish Dripping: What to Do
Steam or suspected overheating needs urgent advice. A dripping tundish also needs attention when the hot taps still work. If it continues after the cylinder instructions or a repair, report that history when asking for help. A recurring drip is a reason to investigate the cause, not to keep repeating a reset or order another valve without a diagnosis.
First: is water passing through it or escaping onto the floor?
Describe what you can see without touching the water: a drip falling through the open funnel, water escaping from a connection, or both. If you first noticed an outside pipe dripping, say so. A wider photograph showing the cylinder label and the pipe route is more useful than a close-up of one unknown valve. Do not remove boxing or covers to get it.
Can it wait for an appointment?
Steam, very hot discharge or suspected overheating needs urgent professional advice. If safe, switch off the cylinder heat sources at normal accessible controls. Keep clear, leave the water supply on and never obstruct the discharge. Do not touch it to judge temperature. Follow the exact model’s instructions and explain worsening discharge when arranging help; an existing appointment does not establish that waiting is safe.
Source: Megaflo Eco Plus manufacturer manual: fault finding and warnings (PDF)
You followed the cylinder label, but it is still dripping
A DIYnot resident traced an outside drip to the tundish and reported that following the label had not stopped it; the discussion gives no confirmed repair outcome. This is a useful point to stop and seek model-specific advice. Record what instruction you followed and whether the behaviour changed. Do not keep repeating an unfamiliar procedure because a video says it should take longer.
Is an air-gap recharge always the answer?
No. Baxi publishes a homeowner air-gap procedure for applicable Megaflo cylinders and directs persistent dripping to a G3-qualified installer. Other arrangements use an external expansion vessel. Identify the exact model before using instructions: an air-gap procedure is not a general repair for every unvented cylinder. If you cannot identify the equipment, stop and ask. This guide does not walk you through operating safety valves.
A plumber replaced a valve and the drip came back
Tell the repairer that the original symptom has returned and provide the date, invoice and part description if available. Note whether the drip is continuous or appears during normal heating, without restarting equipment with a suspected safety fault. Ask what the first assessment established and what the next visit will check. A DIYnot poster reported recurrence the morning after work and a planned return visit; the final cause remained unconfirmed in the thread.
Source: Public homeowner report: discharge returned after a visit (DIYnot, 2023; no confirmed final fix)
Book for cylinder work, not just a boiler check
Say “unvented cylinder” when enquiring, even if you normally call the whole cupboard the boiler. Ask whether the attending person is competent to work on that cylinder and whether you are booking a fault assessment or routine maintenance. Describe previous visits, including work on the boiler that did not address the cylinder. You should not have to identify a faulty part before asking for the right appointment.
What information makes a repeat visit more useful?
Keep one short record: when you first noticed discharge; whether it has changed; the cylinder model; any recent service or repair; and whether water is also escaping onto surfaces. Add access arrangements, especially for a locked cupboard or managed building. Ask how assessment charges, further parts and a possible return visit are authorised. If you rent, send the same record to the agent so each person receives the same account.
Does the whole cylinder need replacing?
Ask for the finding that supports replacement. A symptom report alone is not a comparison of a component repair with a new cylinder. Request the repair option, replacement scope and reason one is unsuitable before deciding. If there is immediate danger or active damage, obtain urgent advice first rather than delaying it to gather competing quotes.
Common questions about this
Can I cap the pipe to stop the drip?
No. Keep the safety discharge route open. Ask for the cause to be investigated; blocking its outlet is not a repair.
The hot water still works. Does that mean the drip is harmless?
Do not use a working hot tap as reassurance about a separate discharge. Report the drip and follow the instructions for the cylinder, particularly if discharge is continuous or overheating is suspected.
Should I book servicing or report a fault?
Report the active drip and any earlier repair when booking. Ask whether the visit covers diagnosis, routine maintenance or both, and how additional work will be agreed.
Related repairs and advice
Where to go next
If this matches what you are dealing with, our water heaters pages explain the service and how to request an assessment.