Start with the installation history, not another cleaner
A newly finished bathroom should not leave you repeatedly masking a sewage smell. The useful first question is what changed between the last normal use of the old bathroom and the first occurrence in the new one. A replacement shower waste, moved toilet or newly enclosed pipe creates a different investigation from a bathroom that was simply redecorated.
Timing is evidence, but it is not a verdict on the installer. An existing drainage problem can become apparent during a renovation, and a component removed for cleaning can also be relevant. Describe the sequence without deciding in advance which person or product must be responsible.
This guide helps you prepare a snagging report and a productive return visit. It does not diagnose concealed connections from a photograph or establish whether building work complies with regulations. The aim is to identify the next inspection that can explain the symptom, with as little unnecessary disturbance to the new room as possible.
Decide whether this can wait for a routine return visit
If wastewater is coming back through a fixture, stop using the affected arrangement and arrange prompt drainage assistance. Do not keep flushing to demonstrate the problem. Fresh water escaping into the floor or the room below also needs attention before a routine snagging appointment, particularly if electrical fittings are affected.
A smell described as sewage is not a reliable way to exclude another hazard. If you suspect gas, burning or an electrical fault, stop these checks and seek the appropriate emergency assistance. Do not enter a drain, service void or other confined space to trace an odour.
For a recurring smell without backup, visible leakage or other urgent signs, contact the installer with a written account. Give the date of completion and explain whether the symptom occurs every day, only after use or after the room has been unused. That makes the booking more useful than asking someone to visit when the smell happens to have disappeared.
Reconstruct what was changed and what was retained
Look through the quotation, product receipts and any photographs taken before the walls were closed. Mark each bathroom fitting as new, moved or retained. Include the basin, bath, shower, WC and any former connection that is no longer used. A room with new sanitaryware can still have much of its original waste pipework.
Record whether a bath became a shower, whether the WC moved across the room and whether a vanity unit replaced an exposed basin. Note new boxing, a concealed cistern or a tiled panel. These are access facts for the investigator, not proof that the concealed section is defective.
Ask the installer to identify the route from each changed fitting to the main drainage connection. A simple marked photograph is adequate for an initial discussion. If nobody has an accurate drawing, label the route as unknown instead of filling the gap with an assumption about where a pipe probably runs.
Keep a separate list of changes made after handover. Examples include someone removing a shower insert, a cleaner using a drain product or another contractor fixing furniture around a pipe. The return visit should consider the actual current installation, including work performed after the original plumber left.
Build a short chronology that can be checked
Start with the last day the old bathroom was used, the first day the new fittings were used and the first noticed smell. Record any period when the property was empty. If the odour was noticed before anyone used the new shower, say so; that is different from a symptom beginning after several showers.
| Record | Useful example | Why include it |
|---|
| First occurrence | First evening after handover, before shower use | Separates initial installation conditions from later use |
| Ordinary trigger | Noticed after the upstairs WC was flushed | Identifies a sequence worth observing |
| Location | Strongest near the vanity opening | Helps choose accessible inspection points |
| Associated evidence | Gurgling, slow emptying or a fresh damp mark | Distinguishes odour from flow and water-loss symptoms |
| Previous action | Shower grid cleaned; smell returned next morning | Prevents the same maintenance being repeated without explanation |
One or two clear entries are better than weeks of vague recollection. Use normal household activity only where the fittings remain safe to use. There is no need to run every tap together, fill a tray to its edge or recreate a backup for a video.
If the smell follows flushing, our flush-triggered sewage-smell guide gives more detail about that pattern. Keep the renovation chronology alongside it so the contractor knows which connections were recently disturbed.
Identify the shower waste before removing anything
A decorative grid does not identify the complete trap underneath. Find the waste model from the invoice, packaging or installer, then obtain its own maintenance instructions. Do not assume that the visible opening should contain the same insert as a previous shower or a photograph found online.
For example, McAlpine's L-STWR instructions show a removable dip tube and require it to be replaced after cleaning. They also warn against chemical drain cleaner and damage to the dip-tube seal. Those details apply to that product family; they are a reason to check the actual model, not to fit a generic part into any waste.
Ask whether all intended components were present at handover and whether anything was removed during the final clean. Keep any loose part found in a cupboard or packaging and photograph it. Do not force it into the opening merely because it appears to fit.
If cleaning has already been attempted, tell the installer exactly what was removed and replaced. A short description such as “only the decorative grid was lifted” is more informative than “the drain was checked”. The guide to shower smells after cleaning covers that maintenance question separately.
Check the waste arrangement, not just the visible finish
England's Approved Document H addresses traps that prevent foul air entering the building, access and ventilation for air admittance valves, and air tightness of sanitary pipework. These are useful subjects for a professional inspection. Reading the document does not establish that a particular bathroom passes or fails.
Ask the installer which joints and trap components were checked, and how. A reply that the tiles and silicone look sound does not describe an inspection of the drainage connections. Equally, a neat-looking installation should not be condemned simply because the symptom has not yet been explained.
For a moved WC, ask whether the pan outlet connection and its route can be inspected through existing access. Do not pull the toilet forward or rock it to test the joint. Record any movement noticed during normal use and let the installer determine whether support or connection work is needed.
Adding a cosmetic seal around a fixture is not a documented repair to an unidentified waste defect. If sealing is proposed, ask what problem has been found, which connection the work addresses and how the result will be checked. This keeps finishing work tied to a diagnosis rather than merely hiding an opening where the smell was noticed.
Ask what happened to ventilation and access
A new vanity or pipe enclosure may contain a drainage valve that was previously exposed. McAlpine describes an air admittance valve as allowing air into drainage while preventing foul gases escaping. It is a drainage component, separate from the bathroom extractor fan.
Ask the installer whether an air admittance valve is present, where it is and which product was fitted. Request the access and ventilation arrangements to be explained using the product instructions. Do not block openings, wrap the valve or pack the enclosure with insulation to suppress the smell.
The presence of a valve does not prove it is faulty, and replacing it is not automatically the next step. The investigator needs to consider the altered pipework and the observed symptom together. If the proposed work is simply “try another valve”, ask what inspection makes that a reasonable choice.
Record whether a panel is removable and who knows how it is fixed. A concealed fixing can easily be damaged by someone assuming the panel pulls straight off. Ask for the intended access method before allowing a new tiled or decorated surface to be opened.
Keep the wider drainage system in the enquiry
The room is new, but the drains serving it may not be. Ask whether another bathroom, kitchen or neighbouring property is experiencing slow emptying or wastewater backup. These observations can change who needs to investigate without establishing responsibility by themselves.
Thames Water's blockage guidance includes difficult flushing, slow emptying and bad smells among possible warning signs. Where water returns or several fixtures are affected, describe the wider pattern when seeking drainage assistance rather than treating the issue solely as a new shower problem.
Do not assume renovation debris is in the drain without evidence. If a contractor proposes a camera survey, ask which section it will inspect, what question it should answer and whether a recording or written finding will be supplied. A survey of an underground section does not automatically inspect every above-ground bathroom connection.
Likewise, a clear result from one inspection should be recorded with its boundaries. “Accessible waste joints checked” and “entire drainage system tested” are different statements. Precise boundaries make a second investigation more focused when the first does not resolve the smell.
Send a snagging message that requests a useful outcome
Keep the initial message factual and short enough to read before the visit. Include completion date, first occurrence, affected location, normal-use triggers and any visible water. Attach a room overview and a small number of clear photographs of accessible fittings or staining.
An illustrative message is: “Since the bathroom was completed, a sewage smell has returned near the vanity after normal use. There is no visible backup. Please inspect the altered waste connections and confirm the trap and ventilation arrangements. Please also explain any access needed before opening the new finish.” Adapt this to what you actually observed.
Ask who will attend and whether they have the installation information. A person arriving only to clean the plughole may not be equipped to inspect concealed connections. The appointment should match the unresolved question and identify who can authorise further access.
For a rented property or managed flat, send the same evidence to the landlord or managing agent through the usual reporting route. Identify any shared services or access through another room. Keep copies of replies and appointment notes; this guide does not determine payment disputes, contractual liability or who ultimately pays.
Agree targeted access before disturbing the new bathroom
Before tiles, cabinetry or boxing are removed, ask what the proposed opening is expected to reveal. The answer should name a fitting, joint or pipe section rather than simply say that everything must come out. Existing service access and installation photographs may help narrow the work.
Agree who protects adjacent surfaces, who opens the enclosure and who restores it afterwards. Where waterproofing or specialist finishes are involved, ask how their reinstatement will be addressed. Do not drill exploratory holes yourself; the hidden space can contain more than the waste pipe you are trying to inspect.
Ask for photographs of any defect before repair, where practical, and an explanation of what was changed. Retain the product details of replacement fittings. A record of the original finding and the repair is more useful if the symptom returns than a receipt saying only “bathroom works”.
If access does not reveal the expected problem, pause to review the next step. Further opening should have a fresh reason based on what has now been seen. An inconclusive first opening is not, by itself, evidence that a larger area needs removing.
Make the completion check match the original complaint
At the end of the visit, ask for a note of the observed fault, work completed and checks performed. If no fault was identified, the note should say what was inspected and what remains uncertain. Avoid accepting a definitive explanation that the attending person has not actually established.
Compare the result with the original normal-use sequence once the professional confirms the fittings can be used. If the smell previously appeared the following morning, an odour-free room immediately after the repair is encouraging but does not reproduce that timing. Keep a short follow-up record rather than masking the room with fragrance.
If the symptom returns, report the same location and sequence alongside the repair note. Mention any change, such as the smell now appearing without shower use. This gives the next visit a starting point and reduces the chance of repeating a check that has already answered its question.
For a smell-only complaint after installation, start with the bathroom installer or a plumber able to investigate the waste arrangement. A drainage restriction needs an appropriate drainage service. We do not provide drain unblocking, and odour alone does not justify booking a hidden water-leak search.
If the renovation has left escaping water, repeated dampness or leakage into the room below, send us the installation history and photographs. Our water-leak repair service can be discussed around locating the water loss, repairing affected pipework and making good the access required.
Our fixed hourly rate is £150 per hour; the total depends on the work needed. If we do not find the leak, you do not pay for the time spent looking. Read the pricing and scope and explain any previous inspections so the enquiry starts with the remaining water-leak question.
