Boiler low pressure wont re-set.

[keel]

Hi, I have a Worcester Bosch 350 combi boiler. Yesterday the low system pressure light came on. The pressure was low so I pressured it back up to normal but the low pressure light has stayed on and of course boiler wont fire up. Has anybody got any ideas on what I can do? All advice gratefully received. Thanks

 

[gas4you]

Could be a faulty pressure gauge, or perhaps a small bit of crud blocking the pressure sensing tube.

Try over pressurising it VERY temporarily and see what happens.

 

[keel]

Thanks Dave, How high dare I pressure it to?

 

[gas4you]

As high as you like, the PRV will open at about 3 bar, so you won't do any damage to the boiler.

Probably won't cure it, but a simple thing to try first.

 

[keel]

Hi Dave, took pressure up to 3 bar but light has stayed on. Is switch an easy item to replace?

 

[gas4you]

Everything on any WB is a pain in the bum. I will only service them, anything else I walk away, no charge to customer.

 

[stevies62]

Sounds like the water pressure switch is blocked. Drop the pressure in the system and remove it. It's a round thing about 1 and half inches at the left hand side of the pumps. Use a matchstick or an allen key to push the crud out, check the pipe connection as well.

 

[Steve69the69Gas]

Have you tried simply resetting it - power off - back on after a few secs?

 

[Agile]

If the pressure sensor inlet is blocked then they usually do eventually reset after up to a few hours with a rather high pressure of say 2 BAR.

I usually ask my customers to wait 2-3 hours and then I would come and replace it or better still if they are not too bothered I suggest they leave it overnight.

Of course there is a very important question of why the owner does not regularly check the boiler pressure BEFORE the LP switch operates!

Tony

 

[Aquaheat]

Have you also checked that the overheat stat has not tripped? Top right of the boiler.

Until you get the switch repaired or replaced, as a VERY temporary measure, you can switch the white and the green wires on the low pressure switch and it will give you heating and hot water but like i say this should only be used as a very temporary measure and is not a fix!!

 

[keel]

Thanks for all advice. Tried all except shorting the wiring. Was going to try this but tried giving it a few 'taps' with hammer & screwdriver. After a dozen 'taps' it reset itself.Thanks again for help.