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Strange goings on with a combi boiler


Harry136
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Hi,

In our house we have a Vokera Vision 30c combi boiler, the pressure needs topping up every couple of weeks.

Obviousley we have a leak somewhere, the weird thing is, throughout summer, the boiler retains its pressure!

Any ideas what could be going on and what i could do to solve it?

There is no sign of any leaks anywhere!

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There are 3 reasons why a combi boiler will loose pressure.

  1. The expansion vessel air charge is depleted. This happens naturally and is easily checked and amended, or it could be that the diaphragm has ruptured (tell tale sign is water fro mthe air valve).
  2. The pressure relief is letting by - Check outside to see if it is continually dripping.
  3.  You have a leak on the system somewhere. it's not easy to find especially if you have pipe running under solid floors. I would check and eliminate the first 2 before you look at this option. 

Hope that helps.

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I made the mistake of topping up with water every time the pressure dropped, putting it down to a leak! It WAS a leak, but not a water one! I noticed one day the pressure guage went into the red when the heating was on! Dropped the water via the full valve and re pressured the expansion vessel using a bike pump. Now I have replaced the shrader valve and it’s perfect! 

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I had a similar problem and suspected the older, original copper piping on the heating system. I drained the towel rail in the bathroom, added some Fernox leak sealer, then refilled the system. That sorted the problem. I shall now await the bombardment from heating engineers telling me how my system will soon be blocked up and it will need the entire thing ripping out and starting again. A bit like British Gas telling people, especially the elderly, that their boiler needs replacing, which, of course has nothing to do with the commission they will get,  if the job goes ahead  !

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46 minutes ago, B725 said:

Not from me, Fernox or Sentinal internal leak sealer can help seal the tiniest of leaks that are hard to find I've used it a few times 

I also used it on my Daughters heated towel rail that developed a drip from one of the tube welds (a month out of warranty). Stuck the Fernox in, topped up water, left towel rail off for a day and turned it back on. Two years later and it is still going strong  !

1 hour ago, Harry136 said:

Hi,

In our house we have a Vokera Vision 30c combi boiler, the pressure needs topping up every couple of weeks.

Obviousley we have a leak somewhere, the weird thing is, throughout summer, the boiler retains its pressure!

Any ideas what could be going on and what i could do to solve it?

There is no sign of any leaks anywhere!

Possibly it is a heat expansion leak on the heating pipes/radiators, which do not get used much in the Summer  ?   My leak was.

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6 hours ago, Harry136 said:

Unfortunately I can’t see the outlet pipe as it has been plumbed into the guttering. Would it be same for me to remove the case of the boiler to see if it’s been leaking inside?

Could you temporarily slip a bit of hose or plastic tube over the expansion outlet just while you see what is going on?  I doubt you can see from the inside.

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8 hours ago, Harry136 said:

Unfortunately I can’t see the outlet pipe as it has been plumbed into the guttering. Would it be same for me to remove the case of the boiler to see if it’s been leaking inside?

It's bad practice to put the outlet into the gutter it should be visible at all times so you can see any water being wasted also if it lifted at a high temperature it could damage the plastic gutter. 

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  • 2 weeks later...

Mine was the same I had the boiler cleaned, pipework flush out. I was told only Friday that most combi boilers needed top up anyway, more so in winter. Mine needed doing every 10 days, sometimes less until I had it cleaned last summer and it went from May until December before it dropped pressure. 

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hello, if it is just loosing a bit of water out the over flow and needs a top up every so often i would try some sealant before you get a heating engineer, its not expensive to try first, just drain a bit of water off the radiator that has the out flow valve and once below the brass air plug (leave bleed nipple in) take it out pour the sealant in replace brass plug and top up water, start boiler and let the pump work till rad hot, switch off boiler let rad water settle, top up if needed and see if leak stops, you can get a decent sealer for a tenner,

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