How do I fix low water pressure?

Pressure problems get treated as mysterious, but the diagnosis is simple: isolate whether the restriction is at the outlet, inside your plumbing, or upstream of your property. Ten minutes of checking tells you which, and each has a very different fix.

What you'll need

• Adjustable spanner
• White vinegar or descaler
• Cloth
• Old toothbrush (optional)

Step by step

1. Test every tap in the house, hot and cold separately, and note which are affected.One tap, one temperature, or everything — this single observation does most of the diagnosis.
2. If it's one tap, unscrew the aerator from the spout end.Wrap a cloth around it to protect the finish. It should come off by hand or with light spanner pressure.
3. Soak the aerator in vinegar or descaler for an hour, brush it clean and refit.Limescale and grit clog the fine mesh. This is the single most common cause of one slow tap.
4. If it's only hot water, check the hot water system rather than the supply.In a gravity-fed system, low hot pressure is normal and driven by the tank's height. In a combi, it may be a partly blocked heat exchanger.
5. If it's the whole house, check the internal stopcock is fully open.Anticlockwise until it stops, then back a quarter turn. A partly closed stopcock after previous work is very common.
6. Check any pressure-reducing valve or filter on the incoming main.Filters clog. A PRV can stick. Both are common on newer installations.
7. If the whole house is low and everything internal is open, ask neighbours and call your water company.If neighbours are affected too, it's a supply-side issue and not yours to fix.

Tips

• Check the outside stopcock as well as the inside one — after any external work it may have been left partly closed.
• Fluctuating rather than constant low pressure usually points to supply-side demand rather than a blockage in your pipes.
• Shower heads clog exactly like tap aerators. Soaking one in descaler often restores a shower people assumed needed replacing.
• In an old property, galvanised steel pipework corrodes internally and narrows over decades. Pressure that has declined slowly over years may be that.

Common mistakes

• Buying a pump before diagnosing — Most low-pressure complaints are a blocked aerator or a half-closed valve, and a pump fixes neither.
• Ignoring which taps are affected — It's the fastest diagnostic you have, and it's free.
• Forcing a stiff pressure-reducing valve — They're adjustable within a range — beyond it you'll damage the valve.

Questions people ask