New Build London Property: Plumbing Snagging Checklist for Buyers

Plumbing Snagging in New Build London Properties

New build properties in London have a 10-year NHBC Buildmark warranty, but making the most of that warranty requires identifying defects promptly and reporting them in writing during the correct warranty period. Plumbing defects are consistently among the top snagging items reported in new build completions. Knowing what to look for at handover and in the first two years of ownership significantly improves the chances of having defects corrected at no cost.

Boiler and Hot Water System Checks

Run all hot water outlets and confirm that hot water arrives within a reasonable time. In a new build with a combi boiler, hot water should arrive within 15 to 20 seconds of opening the tap at the furthest point from the boiler. If it takes significantly longer, the pipe run may not be thermally efficient or the boiler output may be undersized for the property.

Check the boiler pressure gauge at rest — it should read between 1.0 and 1.5 bar. Check it again after running the heating for 30 minutes at operating temperature — it should not exceed 2.0 bar. Pressure that rises above 2.5 bar indicates a defective expansion vessel, which is a common new build snagging item that should be reported immediately.

Confirm that the magnetic filter has been installed on the boiler return. New build systems should have a magnetic filter as standard and it should have been flushed before handover. Ask the developer to demonstrate the commissioning documentation showing the system flush and boiler commissioning were carried out correctly.

Radiator and Heating Distribution Checks

Turn the central heating on and allow 30 minutes to reach operating temperature. Walk through every room and touch the top and bottom of each radiator. All radiators should be uniformly hot from top to bottom. A cold top indicates air in the system — bleed the radiator using the bleed key and check again. A radiator that is cold at the bottom but warm at the top indicates sludge or blockage — a system that was not properly flushed before handover.

Check that each radiator has a thermostatic radiator valve (TRV). TRVs allow per-room temperature control and are a standard feature of all new build central heating systems. Confirm that the TRVs operate correctly: set one to maximum, allow 10 minutes, confirm the radiator is fully hot. Then set it to minimum and confirm the radiator cools over the following 10 minutes.

Bathroom and Kitchen Plumbing Checks

Test all taps in bathrooms and kitchen for both hot and cold supply. The cold water pressure should be consistent throughout the property. Check beneath each basin, under the kitchen sink and inside the airing cupboard for any signs of moisture, drips or weeping joints. Small weeping joints on new build pipework are a common snagging item and should be reported and repaired under the NHBC warranty.

Fill and drain each bath and basin. Confirm that the waste empties at a reasonable rate without gurgling or backing up. Slow drainage on a new build usually indicates an incorrectly graded waste pipe or a partially obstructed joint — a defect, not a usage issue.

Test all shower valves and confirm they maintain a stable temperature when another tap or toilet is used simultaneously. Temperature fluctuation indicates either an undersized combi boiler or a thermostatic cartridge that has not been set correctly. Both are defects that should be reported.

Soil Stack and External Drainage

Inspect the external soil stack for correct termination above eaves level and confirm it is properly secured to the building facade. During heavy rain, check that gutters discharge freely and that rainwater downpipes are not blocked with construction debris. New build drainage defects are common and the most serious — a blocked external drain or incorrectly connected soil pipe can cause sewage backup into the property.

NHBC Warranty: Reporting Timescales

The NHBC Buildmark warranty covers developer defects for two years from completion and structural defects for ten years. All plumbing defects identified at snagging or within the first two years should be reported in writing to the developer within the two-year defects period. After two years, the warranty covers structural damage only — a plumbing defect identified in year three will be your cost to repair unless it has caused structural damage. Keep all snagging reports, responses and repair records in a file for the full ten-year warranty period.