Unvented Cylinder Tundish Dripping: What to Record and When to Get Help

A dripping tundish can be easy to overlook in an airing cupboard, particularly if the water disappears down a pipe and no floor is wet. But the visible flow is information about the hot-water installation. The right question is what is discharging and why, rather than how to cover the opening or silence the sound.

This guide explains the observations that help an engineer investigate an unvented cylinder. It is not a procedure for repairing pressure controls, recharging an expansion vessel or resetting an overheating safety device. Identify the cylinder and use its own user instructions. A familiar brand name or a photograph of a similar cupboard does not establish that two installations use the same components.

What the tundish does, and what it does not tell you

The tundish is a visible break in the discharge arrangement associated with the cylinder's safety valves. The Worcester Greenstore manual describes visible discharge routed to a safe location. That visibility is purposeful. Hiding the fitting behind stored items or enclosing it to stop the noise removes information the resident may need to notice.

Water seen there does not automatically prove that the tundish itself is defective. The investigation needs to establish which upstream device is discharging and the conditions causing it. A replacement fitting might address physical damage to the fitting, but it would not by itself explain why a relief device was passing water.

Also distinguish water travelling through the opening from water escaping onto the outside of the pipe or cupboard floor. Describe exactly where you first see it. If a nearby connection is leaking, the water may appear close to the tundish without coming through its normal opening. A clear photograph from a safe position helps the engineer separate those observations.

When to seek urgent help

Continuous discharge that appears very hot, steam, unusual overheating or water spilling outside the intended route deserves urgent attention. Keep people away from the discharge and any affected electrical equipment. Do not put a hand into the stream to measure its temperature, collect hot water in an improvised container or try to stop the flow by plugging the opening.

The Megaflo Eco Plus manual directs users with an unresolved operational fault to switch off the appropriate heat source and contact a competent installer; it specifically says not to turn off the water supply. Its fault chart associates continual very hot temperature-and-pressure discharge with thermal-control failure. Follow your own model's emergency instructions and seek help rather than applying a generic “turn every valve off” response.

If you can safely identify and operate the ordinary user controls described in those instructions, use them to stop heating as directed. Do not approach wet electrical controls, remove a cover or touch unfamiliar wiring. Tell the responding engineer if you cannot safely identify the controls or if more than one heat source may serve the cylinder.

Do not wait for a drip-counting exercise when the installation appears to be overheating or overflowing. The booking description should begin with the urgent observation: “continuous discharge and steam”, for example, if that is what you can actually see. If there is an immediate danger to people, use emergency assistance appropriate to the situation.

Record the pattern without provoking the fault

For an intermittent drip without the urgent signs above, note when it occurs during ordinary use. Does it begin while the cylinder is heating? Does it continue after the normal heating period? Was it first noticed after a service or after changes to the hot-water schedule? These details help the investigation but do not establish the cause on their own.

A short video can show intermittent flow better than a still photograph. Film from a safe position without touching the fitting or moving pipework. Include enough of the surroundings to show which component is being recorded. There is no need to keep heating the cylinder repeatedly just to obtain a more dramatic example.

Observation	What to tell the engineer	What it does not prove
Drips during ordinary cylinder heat-up	When the heating period starts and whether the drip stops afterward	That a particular vessel or valve must be replaced
Flow continues between heating periods	Which normal heating controls are active and how long flow has been visible	That the visible fitting is itself the cause
Water spills onto the floor	Where the water escapes and whether electrics or another property are affected	That simply covering the tundish will solve it
Symptom follows recent work	Date, work completed and the contractor's record	That the recent contractor is necessarily responsible

Keep observations separate from conclusions. “Drips for ten minutes after the scheduled heating starts” is useful. “The pressure reducer is definitely faulty” is a diagnosis that needs evidence. Giving the engineer the first statement leaves them free to test the relevant possibilities rather than repeat an assumption.

An air gap and an external expansion vessel are not the same arrangement

Baxi publishes a Megaflo air-gap procedure for the applicable cylinder arrangement. It links dripping to the need to restore that air space. This does not mean the procedure applies to every product described casually as a “Megaflo” or to every unvented cylinder.

The Eco Plus manual used in this article includes an external expansion-vessel arrangement. That model detail matters before anyone gives instructions about expansion maintenance. Read the actual data label and manual, and tell the engineer whether an external vessel is visible. Do not decide the arrangement solely from the cylinder's colour or a neighbour's recollection of their repair.

If you previously followed a manufacturer-permitted maintenance procedure, report exactly which one, when it was performed and how long the result lasted. Repeating a procedure more frequently is not a substitute for understanding why the symptom returns. Ask the engineer to confirm that it is appropriate for the installed model and that the other relevant controls have been assessed.

Do not press a vessel's air valve, attach a pump or open a relief valve as an informal diagnostic test. These actions can change the system state and expose you to hazards. Knowing the component names is useful for a booking conversation; it does not make internal maintenance or safety-device testing a household task.

Why the engineer needs to identify the source of the discharge

Several pieces of information need to fit together: the cylinder model, the connected heat sources, the expansion arrangement, the controls and the route taken by discharge. An engineer should establish which valve is passing water rather than treat every visible drip as the same repair.

The purpose of diagnosis is to connect the observed symptom to a supported cause. Ask what was checked and whether the proposed repair addresses the cause or only a consequence. If a valve is being replaced, ask whether the conditions that made it pass water have also been considered. You do not need instructions for carrying out those checks yourself to request a clear explanation.

A quotation for an expansion component, a control repair and a change to discharge pipework describes different work. Ask which part is necessary and what finding supports it. A single photograph sent before the visit may help with preparation, but it may not be enough to specify the complete repair.

Book someone with the right cylinder competence

Describe the job as an unvented hot-water-cylinder discharge problem. Ask the provider to confirm competence for the cylinder and its safety arrangements. If separate gas-appliance or electrical work is needed, explain the heat sources so the appropriate skills can be arranged. The fact that someone services a boiler does not by itself tell you the full scope they have agreed to handle on the cylinder.

Have the make, model, capacity and any accessible serial information ready. Photograph the data label without removing insulation or electrical covers. Include the installation date if known and the latest service record. If the cylinder is in a flat, explain concierge, parking and access restrictions that may affect the appointment.

Say whether the home still has usable hot water and whether there is active water damage. In a rented property, notify the landlord or agent promptly and keep a written record. Where a communal plant room or shared route is involved, arrange authorised access rather than operating equipment that may serve other homes.

For local help, our London hot-water-cylinder service is the relevant booking route. Start with the discharge symptoms rather than asking to buy a particular valve. Confirm current availability, the diagnostic charge and the process for approving further work.

Questions that make the quote easier to compare

Ask whether the initial price covers a defined inspection, an hourly attendance or a specific repair already justified by earlier findings. Clarify VAT, parts, access work and any return visit. If the cupboard is difficult to reach or pipework is boxed in, describe that before booking; an otherwise reasonable quote may depend on access that the contractor has not seen.

Ask what happens if the fault is not present during the visit. A history and video can help, but the engineer may still need further observation or a different investigation stage. Agree how additional time is authorised and what written findings will be provided.

If you have an existing warranty or maintenance agreement, contact the provider before commissioning non-urgent work that you expect them to fund. Record their instructions and job reference. A warranty decision belongs to that provider; a general article cannot guarantee cover for a discharge fault or a replacement component.

Keep the discharge route visible and unobstructed

The manufacturer's safety guidance is explicit that discharge pipework must not be blocked or repurposed. Do not cap it, attach an improvised restrictive hose or seal the tundish to stop smells or splashing. If the discharge route creates a nuisance, ask for its condition and arrangement to be assessed as part of the job.

Do not store towels, cardboard or cleaning products where they hide the fitting or interfere with access. Keep a safe viewing position available. If a resident cannot readily see or hear a discharge, tell the installer so they can assess how a problem would be noticed in that home.

A complaint about odour at the tundish is also worth describing separately from the water discharge. Avoid fitting an improvised trap or valve based on a sink-drain solution. The engineer needs to consider the specific hot-water safety discharge arrangement, not treat it as an ordinary waste connection.

What to ask for after the visit

Keep a record of the component or condition found, the work completed and the checks performed before the cylinder returns to normal use. Ask whether any restrictions remain and which ordinary controls should be used. If further work is needed, agree who is responsible for arranging it and when.

Ask the engineer to identify the exact manual and model-specific maintenance expectations. Keep those with the service history. If a user procedure is demonstrated, record its boundaries as well as the steps: when it is appropriate, when it is not and what symptom should prompt another call.

If dripping returns, describe whether it matches the original timing and refer to the earlier invoice. Do not silently restart an escalating sequence of adjustments. A clear follow-up record helps the contractor reassess the same installation without losing the history of what has already been tested or changed.

Common questions about a dripping tundish

Is a small drip harmless because it reaches the drain?

The absence of a wet floor does not explain why water is being discharged. Report recurring flow and arrange an assessment. The route carrying the water away is doing a different job from the controls that determine when discharge occurs.

Will replacing the tundish stop the problem?

Only inspection can establish whether the fitting itself needs work. Ask the engineer to identify the upstream source and reason for the discharge. Replacing a visible component without addressing a separate cause may leave the original symptom unchanged.

Can I use a Megaflo air-gap guide on another cylinder?

Do not assume so. Identify the exact manufacturer and model, then use its instructions. Some arrangements use a separate expansion vessel. A procedure intended for another design can be inappropriate even when the cupboards look similar.

Should I turn off the mains water to stop hot discharge?

Do not apply that as a generic cylinder-fault remedy. The cited Eco Plus user guidance expressly says not to turn off the water supply for the unresolved fault it describes. Follow the correct model's shutdown instructions, stop the heat source safely as directed and obtain urgent professional advice for hot continuous discharge.

What if the dripping stops before the appointment?

Keep the photograph or video and explain when it happened, which heating period was active and whether anything was changed. Contact the provider with the update. Intermittent behaviour still needs an accurate account rather than being treated automatically as a resolved fault.

Has the hot water also stopped?

Report that alongside the discharge rather than treating it as an unrelated fault. Our unvented-cylinder no-hot-water guide explains the distinction between cold water, reduced flow and a heating problem. Safety discharge still takes priority over ordinary control checks.

Megaflo expansion arrangements

The Megaflo air-gap guide distinguishes internal air-volume designs from external expansion vessels. Match the model before following recharge advice, and seek competent assessment if discharge continues or overheating is suspected.