Combi boiler pressure dropping?

longwalks1

My Worcester Bosch combi boiler is about 7 years old now (Junior 28i model), and the pressure dial/gauge when not in use sits between 0.5 bar and 1.2-3 bar. Was always told it had to be a minimum of a certain pressure. It had a pipe for 'topping it up' which I have to do a couple of times a year, is this normal?

To me it looks as though its 'losing pressure' over time, is that normal??

rockin_plumber

Pressure dropping would indicate a leak on the system somewhere.

The topping up facility is really for initial filling of the system not regular topping up, as this would indicate a leak.

Introducing fresh water regularly dilutes the inhibitor in the sysyem, which protects the system.

Topping up is a temporary measure, finding where the water pressure is going is the only solution.

Ectophile

Most combi boilers are supposed to be pressurised to around 1.0 bar when cold. The pressure may rise a bit when the heating is on.

If it rises over 3.0 bar, then a pressure release valve should open, to prevent the system bursting. If this happens, the pressure will be lower when it cools down again. This shouldn't ever happen in normal use, and suggests a failed expansion tank.

On the other hand, if you just lose pressure gradually over a period of months, it suggests a slow leak.

longwalks1

Thanks guys
I'm assuming in a slow leak you mean a physical loss of water? Or it venting off somewhere?

Cheers

Myser

Can be from a radiator valve, joint in pipework or even to a device inline with the pipework say a zone valve etc.

Ectophile

If it's just gradually dropping, over a period of months, then you have a very small leak somewhere in the system. Unfortunately, it could be almost anywhere. It will mostly leak when the system's hot (because that's when the pressure is highest), so you may never even see it - the water can evaporate away as fast as it leaks.

It's worth checking for damp around the radiators, particularly at the joints on the ends. As the radiators rust away from the inside, those are the first places to go.

Also check that water isn't dripping from the overflow connected to the pressure relief valve. These can stick open. Don't confuse that with the condensate pipe if it's a condensing boiler - that's supposed to drip.

Otherwise, unless you're prepared to rip up the floorboards, there's not much you can do but live with it until the leak gets big enough to cause a problem.

Leif

It may pay to bleed the radiators and then make sure you tighten the bleed valves properly. I had a 'leak' which disappeared after tightening the bleed valves.

I've always reckoned rightly or wrongly that it is best to have a lower pressure, about 1 bar max say, as higher pressures put more strain on the joints and seals in the system.

keystone

Leif wrote: »

It may pay to bleed the radiators and then make sure you tighten the bleed valves properly. I had a 'leak' which disappeared after tightening the bleed valves.

Thats correct. Shouldn't confuse a very gradual loss of pressure over some time with the loss of a large volume of water. Check your bleed valves as said but also the nuts on the rad valves. Other possibilities:

1. Expansion vessel needs recharging.
2. Internal leak between CH and DHW sides of HEX.

Unlikely to have been the result of the PRV lifting. You would see a far greater pressure loss over a shorter period of time IMO.

When was it last serviced?

I've always reckoned rightly or wrongly that it is best to have a lower pressure, about 1 bar max say, as higher pressures put more strain on the joints and seals in the system.

Around 1 - 1.2 bar when cold is right.

Cheers

hellokitty08

My boiler always has low pressure and has done for 8 years, this is even thought it was replaced 3 years ago. I blead the radiators every year and I just top up the pressure every now and again. Water bill is still £20 a month, so I dont think there is a water leak anywhere. I wouldn worry too much.

50Twuncle

We too have an identical problem with an identical (model and age) of boiler - could there be a fault with the boiler ?

diywhynot

They're both WB.;)