Gas Bolier Pressue problems

squrm

Hi,

Looking for advice please, I have a Vokera Mynute gas boiler. The pressure gauge is in the range 0 – 3.5, with 0 – 1 red & anything over 3 red also. For the past couple of weeks when I turn the heating on the pressure goes from just above 1 to just under 3 (red zone) quite quickly, then drops down to 2.5 or so for the duration while on. Once I turn it off the pressure gauge drops all the way down to zero (until I can see it no more) & the red alarm light comes on. It takes approx 2 hours until the pressure gauge slowly makes its way back up to where it should be (between 1 – 1.5 on the gauge). Once its back to where it should be I can reset the alarm & will work normally again.

This only happens when the radiators are on (i.e. if I turn the supply off to the rads the pressure rises slightly when the boiler is on but only minutely, as it always has done. It doesn’t drop right away again once turned off)

Any suggestions for a complete novice before I organise a plumber? Is it something like a sensor is faulty or something bigger?

squrm

bump, anybody?

Sparkpea

Gas boilers isn't my forte but it does sound like a parts problem.

Joey the lips

Have not a clue... Why dont you phone vokera and ask them can they explain the problem before a plumber comes out and tries to rip you off...

Obv you dont know that about the plumber but just say that you hear that vokera are great boilers and this problem no one understands...

I usually find they defend themselves by explaining the problem..

Pete67

It sounds to me like the expansion vessel has either failed or has lost its charge. As far as I remember the Mynute is a system boiler, so the expansion vessel is built in.

If all the water in the system is heated (radiators on) there will be more thermal expansion and the pressure will rise quite quickly if there is no means to absorb the increased water volume. Eventually the pressure relief valve will open and release some of the water and drop the pressure - the relief valve usually operates at around 3.5bar.

When the boiler is switched off, the water cools and contracts and the pressure drops significantly, maybe to zero or even a slight vacuum. The system is now low on water and if it is designed to fill automatically by means of either a mains water supply with PRV or a header tank the pressure will rise back to the setpoint of the PRV, or the gravity head suppled from the tank. The whole cycle will then repeat next thime the heating is switched on.

You can confirm this by looking at the outlet of the pressure relief valve in the boiler, it should be piped through an outside wall (usually 1/2 inch copper pipe somewhere near the boiler. The drain should be dry and no water whould be released from a properly operating system ewhen heating up or in use.

You should get this sorted out quickly, as the constant topping up of water will cause corrosion and sludge build up which will lead to internal rust problems in the radiators, and possible failure of the boiler due to sludge build up in the heat exchanger. Allowing the system pressure to drop to zero can also result in air being drawn in which increases the risk of corrosion and prevents radiators from heating properly or at all.

Hope this helps, a good plumber will identify the issue quickly and advise accordingly.

squrm

Thanks folks