Intro

On most jobs, plumbing work looks simple until the walls open. Then you face tight voids, old pipe runs, mixed materials, and a client who wants water back by 5 pm. This guide breaks down plumbing work into clear steps. You’ll plan the route, choose the right sizes, install cleanly, and test without drama. We cover common UK practices and simple numbers you can use today. You’ll also see how to tidy your paperwork, so quotes, variations, and invoices don’t slow you down. Keep it practical, keep it safe, and keep the client happy.

Quick Answer

Plumbing work means planning the route, sizing pipes, installing first and second fix, then pressure testing and commissioning. Aim for correct falls on wastes, solid clips, safe temperatures, and a clean handover. Use clear proposals and signed approvals to prevent disputes and protect your margin.

Table of Contents

• Plan Plumbing Work The Right Way
• Materials, Sizing, And Code Basics
• Step-By-Step: First Fix To Final Fix
• Pressure Testing And Commissioning
• Common Mistakes In Plumbing Work (And Fixes)
• Paperwork That Wins Jobs (Quotes, Variations, Invoices)
• FAQ

Key Takeaways

• Set waste falls at about 1:40 (25 mm per metre). Don’t go flatter than 1:80.
• Store hot water at 60°C. Target outlets at 50–55°C with mixing.
• Clip 15 mm copper at ~1.2 m horizontal, 1.5 m vertical; plastic closer.
• Test at 1.5× working pressure or as per spec. Hold for 10–30 minutes.
• Get signed approvals before extra work. Variations save margins and headaches.

Plan Plumbing Work The Right Way

Good plumbing work starts with a simple plan. Walk the route. Measure every run. Note joists, steel, and no‑drill zones. Mark boiler, cylinder, manifolds, and shut‑offs. Take photos before you close anything.

• Map services. Keep hot on the left, cold on the right. Crossings are fine, but plan them.
• Protect trap seals. Aim for 50 mm water seals on most fixtures; 75 mm where airflow is tricky.
• Allow for movement. Pipes expand when hot. Leave 5–10 mm slack on long runs.
• Plan access. Put isolating valves where a hand can reach, not just where it fits.
• Time the work. First fix for a small bathroom often takes 1–2 days. Full house re‑pipe can run 3–5 days.

When you’re on site, simple drawings help. A pencil sketch with lengths and fittings beats guessing later. Add notes for “professional proposals” and “project timelines” so your office team can build a clean quote and schedule.

Materials, Sizing, And Code Basics

Material choice depends on the job. Copper, PEX/barrier plastic, and push‑fit all have a place.

• Copper: Rigid, heat‑proof, clean joints. Clip 15 mm copper about 1.2 m horizontal and 1.5 m vertical. Scale up clips as diameters grow.
• Plastic (PEX/MLCP): Fast, flexible, fewer joints. Clip tighter: around 0.5–0.6 m horizontal and 0.8–1.0 m vertical for 15–22 mm. Use inserts.
• Brass and approved fittings: Stick to WRAS‑approved components. Mix metals with dielectric breaks when needed.

Sizing is simple if you think in flow:

• Showers like 8–12 litres per minute. A single 15 mm supply often works, but long runs and many bends can starve flow.
• Kitchens want steady 10–12 l/min.
• Keep main cold feeds 22 mm into cylinders and manifolds; branch down to 15 mm for outlets.
• Mains pressure commonly sits around 2–4 bar. Some appliances need at least 1 bar. Add a booster if the site is low.

Waste and soil fall matter. Aim for about 1:40 (25 mm per metre). Don’t go flatter than 1:80. Too steep also fails; water outruns solids. Vent the stack to protect trap seals.

Temperature and hygiene:

• Store hot at 60°C to control Legionella. Target 50–55°C at taps via mixers.
• Keep cold below 20°C. Insulate hot and cold lines to prevent heat transfer.
• Use TMVs in bathrooms where scald risk is high.

Always check local rules. In England and Wales, follow the Water Supply (Water Fittings) Regulations and relevant British Standards (for example, BS EN 806 and BS EN 12056‑2). Keep paperwork for inspections.

Step-By-Step: First Fix To Final Fix

Follow these steps for tidy, reliable plumbing work.

1. Survey And Mark-Up

   • Measure runs, note penetration points, and mark centres at 1000 mm for basin mixers, 750 mm for shower mixers, or to client spec. Photograph everything.

2. Isolate And Drain

   • Shut off mains. Open low taps to drain. Pump down heating circuits if needed.

3. Set Brackets And Clip Lines

   • Install sturdy clips at the right spacing. Avoid sagging. Keep pipes straight and level.

4. Run First-Fix Pipework

   • Use sweeping bends where you can. Keep hot on the left. Maintain fall on wastes: about 1:40. Protect pipe where it passes through timber or brick.

5. Pressure Test The Rough-In

   • Cap ends. Fill and purge air. Test at 1.5× expected working pressure or to spec (often 2–3 bar on domestic). Hold 10–30 minutes. Fix leaks now.

6. Insulate And Protect

   • Fit 19–25 mm insulation on hot and primary returns. Sleeve pipes in screeds and at penetrations.

7. Close-Up And Second Fix

   • Fit valves, traps, mixers, WCs, and appliances. Set baths level. Use silicone carefully.

8. Balance, Vent, And Flush

   • Bleed air. Balance radiators or UFH loops. Flush heating lines and add inhibitor. Allow 45–90 minutes on a small system.

9. Set Temperatures And Flow

• Show the client isolators, filling loops, and how to bleed a rad. Leave manuals. Take final photos.

Pressure Testing And Commissioning

Testing makes or breaks plumbing work. Don’t rush it.

• Water Test (Common Domestic): Fill slowly and purge air. Pressurise to 1.5× working pressure or follow the manufacturer’s number. Hold for 10–30 minutes. Pressure should settle quickly and stay steady. Any steady drop means a leak.

• Air Test (Selective Use): Some use low‑pressure air for wastes. Keep it gentle and controlled. Follow BS EN guidance where relevant. Soap test joints. Air stores energy; treat it with respect.

• Heat And Movement: Heat the system and re‑check. Expansion can show a weep you missed cold. Retest after one heat cycle.

• Commissioning Checks:

  • Hot at 50–55°C at outlets; cylinder at 60°C.
  • Cold under 20°C after a long draw.
  • Showers deliver the agreed 8–12 l/min.
  • Wastes clear fast and hold trap seals.

Record the numbers. Write the test pressure, duration, and results on your sheet. Photos of gauges help. This file protects you if a problem appears later.

Common Mistakes In Plumbing Work (And Fixes)

Here are issues you see every week, plus quick fixes.

• Flat Or Steep Wastes

  • Symptom: Gurgling, smells, slow drains.
  • Fix: Reset to about 1:40 (25 mm per metre). Don’t exceed 1:20 unless specified. Vent if traps pull.

• Undersized Feeds

  • Symptom: Shower drops when a tap opens.
  • Fix: Run 22 mm to the bathroom manifold. Keep bends smooth. Consider a pump or booster if mains is weak.

• Poor Clip Spacing

  • Symptom: Sagging lines, noisy pipes.
  • Fix: Re‑clip. About 1.2 m for 15 mm copper horizontal; 0.5–0.6 m for PEX. Add acoustic clips near bedrooms.

• Mixing Metals Badly

  • Symptom: Green corrosion, leaks over time.
  • Fix: Use approved fittings. Isolate dissimilar metals with dielectric breaks.

• Scald Risk

  • Symptom: Hot outlets spike above 60°C.
  • Fix: TMVs on baths and showers. Set outlets 50–55°C. Store the cylinder at 60°C.

• No Paper Trail

  • Symptom: Unpaid extras, disputes.
  • Fix: Log variations the day they happen. Get a signature before you continue. Use clear “change orders” language.

Paperwork That Wins Jobs (Quotes, Variations, Invoices)

Great plumbing work still needs great paperwork. Clients buy confidence as much as copper.

• Build Clear Proposals

  • Break down scope by room and fixture. Note pipe materials, insulation, and testing methods. Add simple timelines. Phrases like “professional proposals” help clients see value.

• Capture Details Fast

  • On site, talk through the job and take photos. Tools like Donizo let you use Voice to Proposal to turn voice notes, text, and photos into a clean, branded quote. That can save 1–2 hours per small job.

• Get Sign-Offs

  • Send the proposal as a branded PDF with a client portal. With e‑signature integration, clients can approve in minutes. No printouts. No delays.

• Lock Variations Early

  • When scope changes, send a variation the same day. Keep labour hours, materials, and any lead times clear. This pairs well with “pricing strategies” content you may share with your team.

• Invoice Smoothly

  • Convert accepted proposals to invoices in one click using Donizo. Stage invoices for first fix, second fix, and completion keep cash flow steady. Use simple “invoice templates” so every bill looks the same.

FAQ

What is first fix and second fix in plumbing work?

First fix is the rough‑in. You run pipes, set brackets, and cap ends. Second fix is the finish. You fit valves, mixers, WCs, traps, and appliances. You test, flush, balance, and set temperatures. Most small bathrooms take 1–2 days for first fix and 1–2 days for second fix.

What fall should I use for waste pipes?

Aim for about 1:40, which is 25 mm per metre. Don’t go flatter than 1:80 or wastes will hold water and gurgle. Don’t go too steep either or water outruns solids. Vent the stack and protect trap seals at 50 mm (75 mm where airflow is poor).

How long does a full re‑pipe usually take?

For a typical 2–3 bed home, many contractors allow 3–5 days. That covers first fix, testing, second fix, and commissioning. Add time for patching and tiling by others. Old buildings with surprises can add 1–2 extra days.

Should I test with water or air?

For pressurised supply lines, water testing is most common and safer. Pressurise to about 1.5× working pressure or as specified, and hold for 10–30 minutes. Some use low‑pressure air on wastes, but handle air carefully. Follow manufacturer and standard guidance.

How do I price plumbing work fairly?

Break it into tasks: first fix, second fix, testing, and commissioning. List fixtures and allowances for fittings. Add time for protection and clean‑up. Put variations in writing before you start extra work. Clear “professional proposals” and signed approvals prevent disputes.

Conclusion

Strong plumbing work is planned, sized, installed, and tested with care. Keep wastes at about 1:40, store hot at 60°C, clip solidly, and document every change. Next steps:

• Walk your next job and mark every run before cutting.
• Pressure test at 1.5× working pressure and record the result.
• Send a clear, itemised proposal and get e‑sign before starting.

If you want faster paperwork, platforms such as Donizo help you capture details on site, send branded proposals, collect e‑signatures, and convert to invoices in one click. Do the work right, then get paid right. That’s how you build trust and steady margins.

• Cylinder at 60°C. Mixers to safe outlet temps. Showers at client’s preferred flow, usually 8–10 l/min.