Published by Verified Plumbers · Last reviewed: April 2026 · Next review: April 2027

Contents

• Methodology & sources
• The first thing to do before you unpack a single box
• What your surveyor didn’t tell you
• The ten-point plumbing check for a new London property
• Pre-1914 properties — the specific checks that matter
• Buying a previously rented property — the specific risks
• The new homeowner assessment visit — what it covers and what it costs
• What to prioritise in the first six months
• The costs to budget for in year one
• Frequently asked questions
• Related guides
• Find a verified plumber for your new property

The first thing to do before you unpack a single box

Find the stopcock and confirm it works.

That’s it. That’s the single most important plumbing action you can take in the first hour in a new property — before you test the boiler, before you run a tap, before you check anything else.

The stopcock is the valve that controls the mains cold water supply to the entire property. If a pipe bursts, a fitting fails or an appliance floods, the stopcock is what you turn to stop the damage.

A stopcock you can’t locate or operate quickly in an emergency is a serious weakness in the property. A stopcock that’s seized from years of non-use is a serious weakness — because you may not be able to isolate the water quickly in an emergency.

How to find it: In most London properties, the internal stopcock is under the kitchen sink. In Victorian terraces it may be in a different location — under the stairs, in a built-in cupboard, or in a boxed-in void under the floorboards near the front door.

If you can’t find it, ask the seller and check the property information and handover paperwork provided at completion, where stopcock location may be recorded.

How to test it: Turn it clockwise to close, then reopen it gently. It should shut off and reopen without excessive force. If it is stiff or will not move, don’t force it — book a local plumber to free or replace it before anything else. A seized stopcock is not a minor maintenance item — it is a flood-risk weakness in the property.

💡 Pro tip: If the stopcock is stiff but not fully seized, a plumber can often free and service it in a single visit rather than replacing it entirely — significantly cheaper than a full replacement if caught early.

What your surveyor didn’t tell you

A homebuyer’s survey — even a full structural survey — is not a plumbing survey. Surveyors are not plumbers. They look for visible signs of water damage, staining and obvious system faults. They do not pressure-test pipework, inspect inside the boiler, check the condition of the drainage system or assess whether the water pressure is adequate for the shower head you’re planning to install.

This is not a criticism of surveyors — it’s a description of what their role covers. The gap between what a survey reports and what a plumber finds on a first visit is frequently significant, particularly in London’s older housing stock.

What surveys typically miss in London properties:

• Lead pipe sections on the cold water supply — possible in older properties where supply pipes have never been fully upgraded
• Gravity-fed hot water systems with cold water tanks in the loft — sometimes described as “working” even when the pressure is inadequate for some modern shower valves
• Original clay drainage runs under the garden — structurally intact in the survey but accumulating root ingress and silt
• Boilers approaching end of life — a boiler that fires and runs is a boiler that passes a visual inspection, regardless of its internal condition
• Sealed central heating systems with no magnetic filter and years of magnetite accumulation
• Non-compliant plumbing installations from DIY or unqualified work — not visible externally

The new homeowner assessment visit:

A structured plumbing assessment visit from a qualified plumber — typically two hours, £150–£250 in London — covers everything a surveyor doesn’t. In many older London properties, a single avoided emergency callout — at £120–£180 minimum — can cover the cost of the assessment visit. Identifying one significant issue before the first winter typically more than justifies the fee.

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The ten-point plumbing check for a new London property

Work through these in order. The first time you do this it takes around an hour. After that, you know your property.

1. Stopcock — location and operation Covered above. Non-negotiable first check. Location, operation, condition.

2. Boiler — age, type and service history Find the boiler and read the data plate — manufacturer, model, installation date. Open the Benchmark logbook if present — this records every service the boiler has received. If no physical logbook is present, check for a QR code on the boiler casing —

Some boilers may have a digital Benchmark record in place of a paper logbook — the Benchmark app launched in 2021 records installation and service history electronically. Source: benchmark.org.uk. A boiler with no Benchmark record — physical or digital — has an unknown service history regardless of what the seller told you.

Boiler age matters — Many combi boilers are expected to last 10–15 years with annual servicing — though actual lifespan varies by model, water quality and maintenance history. In London’s hard water without mitigation, that lifespan can be shorter. A boiler over 10 years old with no service record in a London property should be assessed by a Gas Safe registered engineer before the first winter.

3. Water pressure — hot and cold Turn on the kitchen cold tap fully. The flow should be strong and consistent. Turn on the hot tap — in a combi boiler property, hot water should arrive reasonably quickly at outlets close to the boiler — longer waits at distant outlets are normal due to pipe run length.

Delays at all outlets, including the nearest, can point to a system design or performance issue worth investigating. In a gravity-fed system, hot water pressure will be lower — this is normal but affects what shower valves and taps will work correctly.

Low cold water pressure at the kitchen tap is worth investigating — it may indicate a partially closed stopcock, a scale-restricted supply pipe, or a supply issue from the street.

4. Hot water system type Identify whether the property has a combi boiler (no cylinder, no tank), a system boiler (cylinder, no loft tank) or a gravity-fed system (cylinder and cold water tank in the loft). Each has different maintenance requirements, different pressure profiles and different implications for bathroom and kitchen specification.

A gravity-fed system in a London property needs the loft cold water tank inspecting — scale accumulation, float valve condition and lagging are all check items that are frequently missed.

5. Lead pipes — cold water supply In older properties, lead pipework may still be present on parts of the cold water supply, particularly where supply pipes have never been fully upgraded. Under the kitchen sink, pipes that are dull grey and soft enough to be scratched with a key may be lead — though a Thames Water assessment will give a definitive answer.

Thames Water operates a lead pipe replacement scheme. You pay for the replacement of the pipe on your land. The scheme allows either an approved plumber who provides certification, or an independent plumber if Thames Water inspects the open trench before it is buried.

Where the private-side replacement passes inspection or certification, Thames Water may replace its section of the supply pipe under the scheme.

Thames Water also uses orthophosphate dosing at treatment works — standard UK water industry practice — which helps reduce lead levels in the supply. Contact Thames Water directly for an assessment of your specific pipes.

6. Central heating — radiators and pressure Turn the heating on and check every radiator. Cold at the top often points to trapped air — bleed it. Cold at the bottom often points to sludge or circulation issues — a system-wide problem requiring investigation. Uneven heating across the property may indicate pump issues, zone valve faults or significant sludge accumulation.

Check the boiler pressure gauge — a sealed system should read between 1 and 1.5 bar when cold. Below 1 bar indicates pressure loss. Check whether a magnetic system filter is fitted to the central heating return — if not, fitting one should be an early priority in any London property. See our central heating repair guide for full diagnostics.

7. Drainage — all outlets Run every sink, bath and shower to waste and watch the drainage speed. Slow drainage usually points to a local blockage or a downstream restriction — worth investigating if multiple outlets are affected. A gurgling sound when draining can indicate a downstream blockage or venting issue and is worth investigating if it affects more than one outlet.

Flush every toilet and confirm the cistern refills promptly and the phantom flush doesn’t activate — water running into the bowl after the flush cycle ends is a fill valve fault.

8. Outdoor taps and garden plumbing Check any outdoor tap — turn it on and confirm flow, then check under the kitchen sink or in the utility room for the isolation valve that controls it. Outdoor taps in London properties are frequently uninsulated and freeze in cold snaps — confirm the indoor isolation valve works so the tap can be isolated before winter.

9. Hard water mitigation — what’s already fitted In a London property, check whether a scale reducer or polyphosphate dosing pot is fitted to the boiler cold inlet and whether a magnetic system filter is fitted to the central heating return. These are the two most important hard water protection measures — and they are frequently absent in London properties because sellers and previous occupants didn’t know to fit them.

If neither is present, fitting both should be among the first plumbing jobs you commission. See our London Hard Water Guide for the full context and mitigation options.

10. Appliance connections — washing machine and dishwasher If the property comes with a washing machine or dishwasher, check the supply hose connections at the back of the machine and confirm isolation valves are fitted on the supply. A machine connected without isolation valves cannot be isolated quickly if a hose fails — a common cause of significant water damage in London flats and terraces.

Pre-1914 properties — the specific checks that matter

London has one of the highest concentrations of Victorian and Edwardian terrace housing in the UK. If you’ve bought a pre-1914 property in Greenwich, Lewisham, Southwark, Wandsworth, Islington or any of the inner south and east London boroughs, the plumbing checks above apply — plus these additional items specific to older stock.

Single-pipe central heating: Some pre-1914 and interwar properties retain single-pipe central heating systems — where all radiators are connected to a single loop rather than separate flow and return pipes. These systems heat unevenly by design — radiators near the boiler are hotter than radiators at the end of the loop. If your radiators heat inconsistently and the system is original, it may be single-pipe rather than a fault. A heating engineer can confirm whether this is the case and advise on zone valve addition or full conversion — both worth considering when the boiler next needs replacing rather than as a standalone project.

Original clay drainage: Victorian terrace gardens frequently have original clay drainage runs connecting to the shared lateral drain. Clay drains are structurally sound when undisturbed — but root ingress from garden trees, ground movement from London clay soil and decades of accumulated grease and silt make them the most common source of blocked and collapsed drains in older London stock. A CCTV drainage survey — £150–£250 — is worth commissioning for any pre-1914 property before problems emerge.

Non-standard pipe runs: Victorian terraces were built before any standardisation of plumbing layout. Supply pipes run through original voids, under suspended timber floors and through built-in furniture. Understanding where the pipes run in your specific property is part of knowing the property — and a general plumber who has visited and assessed is worth more than one attending a first emergency callout blind.

Imperial fittings: Some pre-1914 properties retain original imperial-size pipework — ½ inch, ¾ inch — which requires adaptation fittings when connecting to modern metric components. Not a serious problem, but worth knowing before specifying taps, valves or shower fittings that assume metric connections.

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Buying a previously rented property — the specific risks {#previously-rented}

A property that has been rented out — particularly one managed by a portfolio landlord without a systematic maintenance programme — carries specific plumbing risks that are worth investigating before problems emerge.

Deferred maintenance: Tenant-reported faults that were not fixed promptly, or were fixed cheaply rather than correctly. A property with multiple tenancies and no documented maintenance history may have accumulated deferred repairs across multiple systems simultaneously.

Compliance work not done: Gas Safety Certificates, Legionella risk assessments and boiler services are legal requirements for rented properties — but enforcement is inconsistent and documentation is frequently incomplete. If the property was rented, ask for the last three years of CP12 certificates and boiler service records. Gaps in the record are information. See our London Landlord Plumbing Compliance Checklist for the full compliance framework.

Appliance connections: Previously rented properties sometimes contain appliance connections made without proper isolation valves, standpipes or waste arrangements — regardless of who made the connection. Older supply hoses — particularly those over five years old — are worth replacing as a preventative measure. Both are worth checking and correcting where needed. See our washing machine and dishwasher installation guide for what a compliant connection looks like.

DIY plumbing: Tenants occasionally make their own plumbing modifications — additional shower connections, moved washing machine positions, altered pipework. These are not always compliant with Water Regulations 1999 and are not always visible externally.

A plumbing assessment visit by a qualified plumber is particularly valuable for previously rented properties — the gap between what’s visible and what’s actually been done is frequently larger than in owner-occupied stock.

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The new homeowner assessment visit — what it covers and what it costs

A structured assessment visit is often a cost-effective way to identify issues early and plan priority work. Here is what a properly structured visit covers:

What the plumber does:

• Locates and tests the stopcock
• Reads the boiler data plate and Benchmark logbook or digital record
• Runs a basic boiler diagnostic — pressure, temperature, flue condition, visible scale — carried out by a Gas Safe registered engineer for any gas appliance checks
• Tests water pressure at kitchen and bathroom
• Identifies the hot water system type and assesses condition
• Checks every radiator for cold spots and system pressure
• Runs all drainage outlets and assesses flow speed
• Checks washing machine and dishwasher connections for isolation valves
• Inspects under-sink pipework for lead or corrosion
• Checks loft cold water tank condition if present
• Checks hard water protection measures — scale reducer, magnetic filter
• Produces a written summary: what’s working, what needs attention soon, what can wait

What you should have at the end: A written or clear verbal summary structured as three lists — green (fine, no action), amber (monitor or address within six months), red (address promptly). Any plumber who leaves without giving you this summary hasn’t completed the assessment.

Cost (London 2026): £150–£250 for a two-hour structured assessment. For a Victorian terrace with a gravity-fed system and original drainage, allow two to three hours.

When to book it: Within the first month of ownership — before the first winter if you’re moving in autumn. The assessment identifies issues while there’s time to address them before the heating season begins.

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What to prioritise in the first six months

Not everything needs doing immediately. Here is a realistic priority framework for the first six months in a new London property:

Immediately (day one to week one):

• Find and test the stopcock
• Locate the gas meter and note how to turn it off in an emergency — your gas engineer or Gas Safe Register can advise on safe isolation procedures
• Identify the fuse box and understand the circuit layout
• Book the plumbing assessment visit with a local verified plumber

Within the first month:

• Complete the ten-point plumbing check
• Book a boiler service if the Benchmark logbook shows no service in the last twelve months — or if there is no record
• Fit a magnetic system filter to the central heating return if one isn’t already present
• Fit a scale reducer to the boiler cold inlet if one isn’t already present

Within six months:

• Commission a CCTV drainage survey if the property is pre-1914 with original clay drainage — contact a local drainage specialist
• Address any amber items from the assessment visit
• Check all appliance supply hoses — older hoses, particularly those over five years old, are worth replacing as a preventative measure
• Insulate any exposed pipes in the loft before winter
• Confirm outdoor tap isolation valve is operational before winter

Before the first winter:

• Confirm the heating system works across every radiator
• Bleed all radiators
• Check boiler pressure and top up if below 1 bar
• Confirm all loft pipes and cold water tank (if present) are lagged

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The costs to budget for in year one

These are typical London 2026 ranges. Actual costs vary by property type, access and provider — always obtain multiple written quotes before committing.

Item	Typical London cost 2026	Notes
Plumbing assessment visit	£150–£250	Two-hour structured visit with written summary
Boiler service	£100–£130	Annual — book immediately if no recent record
Magnetic system filter	£180–£280 fitted	Priority one for any property with central heating
Scale reducer (boiler inlet)	£80–£150 fitted	Priority two — hard water protection
Radiator bleed and pressure check	£80–£150	If cold spots identified at assessment
CCTV drainage survey	£150–£250	Pre-1914 properties with original clay drainage
Appliance supply hose replacement	£80–£120	Older hoses worth replacing as preventative measure
Outdoor tap insulation / service	£80–£150	Before first winter
Lead pipe assessment	Free — Thames Water	Contact Thames Water directly for assessment
Stopcock replacement (if seized)	£120–£200	If cannot be freed

Realistic year one plumbing budget for a pre-1914 London property with no recent maintenance history: £600–£1,200 covering assessment, boiler service, filter fitting and two to three priority repairs identified at assessment.

For a modern apartment in good condition with recent maintenance records: £250–£400 covering assessment and boiler service.

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Frequently asked questions

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Data sources:

• Thames Water — Lead Pipe Replacement — lead pipe assessment and replacement scheme
• Thames Water — Hard Water — hard water classifications and London supply data
• Thames Water — Sewers & Drains — shared lateral drain responsibility
• Gas Safe Register — boiler servicing and Gas Safe registration verification
• GOV.UK — Building Regulations — plumbing installation compliance
• Water Supply Regulations 1999 — Water Regulations compliance for new installations
• Benchmark — What is Benchmark — digital Benchmark app and service history records

Review schedule: This guide is reviewed every April. Pricing, technical guidance and source URLs are all verified at each review. The next scheduled review is April 2027.

Reviewed by David, Technical Compliance Editor Verified Plumbers

This guide is based on publicly available UK legislation and official regulatory guidance. It is intended as general information and does not replace advice from a qualified professional where required.

Last reviewed: April 2026 · Next review: April 2027