DIY Doctor

Low pressure - combi

Postby gilly22 » Fri Oct 17, 2008 6:13 pm

Hi there, hoping you can give me some advice in case I can attempt to fix it myself first?

I have a Vokera Linea 24 combi boiler and over the past couple of weeks the pressure drops to 0 and I have to reset it - meaning no hot water/heating.

Once reset I open valve and backfill the pressure to between 1 and 2 and it kicks in ok but maybe later on same day or next day I've to do the same again.

I've checked for leaks and found none. Checked for air in the radiators and again no air. If I kick in the temperature to quite high, all the radiators boost up easily. I've also switched all the radiators off and then turned them on one-by-one and found no problems or unfamiliar noises.

Anything else I can do before I have to call in a plumber? Help please?
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Simply Build It

Postby Steve the gas » Sat Oct 18, 2008 4:45 am

Hi Gilly,

Check your PRV outlet outside, there may be water escaping outside from this. PRV = pressure refief valve goes to outside at same position as bolier.
If water present there = faulty PRV = get a man in.

Steve the gas
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Postby AdamsHeating » Sat Oct 18, 2008 9:47 am

A way to check all combis:

take the pressure of the sealed system up to 1bar. Close off the flow and return isolation valves under the boiler. If the pressure indicator drops, the leak is in the boiler, if it doesn't drop, the leak is on the system, probably a weeping nut on a rad - check thoroughly, underfloorboards etc...

If it is the boiler that is leaking check things like:
Expansion vessel: may need recharging, touch the valve and if you get a wet finger, it will need pumping up or replacing

Pressure release valve: Are you getting a drip to outside?

heat exchanger: you'd probably already know if this was leaking.

Hope this helps,

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Postby chris_on_tour2002 » Sat Oct 18, 2008 9:55 am

do you bleed the radiators after refilling? if not then the trapped air can work its way back to the boiler where it is automatically vented. this will cause a loss of pressure.

failing that, there has to be a leak.
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Postby gilly22 » Sat Oct 18, 2008 5:43 pm

Thanks for these tips, the boiler has been steady today, come on and off on timer ok.... pressure staying 1.5 so will keep an eye on it. Have checked the prv and no leak there, completely dry.

Yes I have bled the radiators after refilling and they are at a constant heat all over - seems fine.

If it goes down again I will check the other options you mentioned like checking under floorboards, hope not, and let you know, thanks,
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