What Should My Boiler Pressure Be? Signs Pressure Is Too High/Low

What Should Boiler Pressure Be?

Boilers lockout when they lose too much pressure, and even when the boiler pressure is too high.

The question is, what should the boiler pressure be?

This quick guide will explain what pressure your boiler should be when it’s hot, cold, optimal working pressures, and how to spot a problem.

It doesn’t matter whether you have a Worcester, Vaillant, Baxi or other brand of boiler, operating pressures are all very similar.

If you’re looking for a professional to help, you can book it here. Or, if you’re tired of your old and unreliable boiler, you can get fixed prices for a replacement on-screen using this form.

What Pressure Should My Boiler Be When It’s Cold?

The boiler pressure should be between 1, to 1.5 bar. Most manufacturers recommend an optimal working pressure of 1.3 bar .

Always refer to your owner’s manual. Different manufacturers will recommend different optimal operating pressures.

Should A Boiler Increase In Pressure As It Heats Up?

The answer is yes. You can check this by looking at the boiler pressure gauge.

This is usually located on the boiler display panel (or just below the boiler casing on some older boilers, such as Ferrolis).

What Pressure Should My Boiler Be When It’s Hot?

Generally, a boiler’s pressure won’t rise by more than 0.3-0.5 bar.

So, it should be no more than 1.5-1.8 bar.

Why Does The Water Pressure Gauge Increase When The Heating Is On?

The pressure on your boiler’s gauge will increase when the heating is running.

The build-up of pressure is caused by water expansion. This is natural, as the boiler heats up water throughout the pipes, radiators and towel rails.

But, your boiler pressure shouldn’t rise more than 1 bar during its heating cycle.

If your boiler heats up more than 1 bar (or close to 1 bar) during start up, there’s a good chance there’s a fault with the expansion vessel or the pressure release valve.

What To Do When…

Boiler Pressure Is Too Low

If your boiler is losing pressure, it may lockout and need to be reset.

Knowing how to repressurise the boiler isn’t hard, simply add water to the system via the external filling loop.

Boiler Pressure Keeps Dropping

This isn’t normal — it’s a sign of a leak. You can figure out why your boiler is losing pressure and leaking here.

Boiler Pressure Is Too High

So, your boiler’s pressure is too high, what do you do?

There’s a good chance you’ve recently topped up the pressure a bit too much.

If you have, you can bleed water from the system via the towel rails as a quick-fix. You’ll need to get a radiator bleed key, a bucket or tub, and some towels. Once you’ve got them, here’s what you do:

  1. Insert the bleed key and open the valve slowly until it starts dribbling water.
  2. Close the bleed valve using the key and check the pressure.
  3. Repeat until you get to optimal pressure.

If you drain too much pressure from the system, you can top it up by using the filling loop to add more water to the system.

What’s Next?

Having problems with your boiler and need them repaired? You can do that here.

Or, do you prefer a quote for a new boiler installation? Head to this form here.

We’re happy to help when we can. If you have any questions, please comment below and we’ll reply as soon as we can.




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  1. The pressure on my boiler says 1.3 on the digital readout cool. But the analogue gauge that replenishes the pressure says 1.7. Which one is correct???

  2. I don’t have a red and green zone so which us the needle to keep at 1.5 the black or the red needle? On boiler for electric central heating

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