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[Crazycarzowner]

Having a problem with ours in that the water pressure gauge keeps going into the red. I filled up the rads, bled them of air as I usually do about this time of year and I thought that would be that. Come 2 days later and the gauge, instead of being in the 'green' bet 1 - 3 bar is in the red? I topped it up again, repeated the process but within a day its back in the red again 
I've looked for the obvious leaks around the rooms but everywhere is bone dry  so I'm struggling now for ideas??
Help!

[Marks DTM Calib]

Check the pressure relief valve, it's the usual culprit and will be venting outside.

[Crazycarzowner]

Sorry for sounding thick but what is one of them & where'd I find it??? 

[Broomies Mate]

Have a gander at the tap you use to fill the system, is it shutting off properly? 

[Crazycarzowner]

Ah!!! Just looked it up on the interweb, think I know why the outside floor is wet now, symptoms stated on the web point at the relief valve being faulty and dumping water through the safety relief valve???  if I've read it right

[tigers_gonads]

Sorry for sounding thick but what is one of them & where'd I find it??? 

The drain is normally a piece of 15mm copper pipe which goes from the relief valve on your boiler, via a hole in the outside wall alongside the flue and vents outside if the pressure gets too high.
If you have a look outside were the flue exits, you will probably see it 
Normally, they are angled downwards so any drips end up on the path outside.

If you remove the cover off the boiler, you will probably be able to see which pipe i'm talking about.
When you have found the pipe / valve, gently t@at the valve with a screwdriver a few times and see if it sorts it out 
If not, the valve will need replacing.
If its a sealed system, you will need to get hold of a flexi pipe and fill the system up until the gauge reads about 1 bar when cold before you do anything else.

[tigers_gonads]

Ah!!! Just looked it up on the interweb, think I know why the outside floor is wet now, symptoms stated on the web point at the relief valve being faulty and dumping water through the safety relief valve???  if I've read it right

Yes   

Must type faster 

[sassanach]

I reckon you need to have a shufti at this
https://en.wikipedia.org/wiki/Expansion_tank
only if this fails will the pressure valve vent.

[tooleater]

If your Pressure Release Valve is dripping it will have failed for a reason. Classic symptom of rapidly rising Gauge is failed Expansion Vessel. Quick test find the Schrader valve on expansion vessel, remove cap and quickly press the pin, if any water comes out the Vessel has failed. Either way you will have to replace PRV

[Shackeng]

I have had one of these stuck slightly open with debris, probably rust scale. I cured it by overcharging the system and allowing a free flow of water for a few minutes. It reseated itself OK afterwards. Yours may be a different design, but worth a try before changing the valve.

[redelitev6]

If your Pressure Release Valve is dripping it will have failed for a reason. Classic symptom of rapidly rising Gauge is failed Expansion Vessel. Quick test find the Schrader valve on expansion vessel, remove cap and quickly press the pin, if any water comes out the Vessel has failed. Either way you will have to replace PRV

exactly what happened to our boiler

[Kevin Wood]

The thing to do is to top up the pressure when cold, then watch what happens next time the system heats up.

If it's set to, say, 1 bar when cold, it would probably be normal to see the gauge rise to 1.5 or even 2 bar when fully heated up.

If it's rising to 3 BAR or more, the PRV will then open and you'll see dripping from the outlet outside. When the system returns to cold, the pressure will be low. These are classic symptoms of a pressure vessel failure.

If the pressure rise is not excessive, but you still have a dripping overflow from the PRV, then the valve has probably failed.

If the system loses pressure but there is no evidence of dripping from the PRV's outlet, then you have a leak elsewhere.

[baggers]

Could be one of a few things.
As mentioned if yours has a flexi pipe for filling the sysyem has it been disconected (it should have been) if not are the isolator valves shutting properly? if they're not this would over pressure the system.

The blow off pipe is 15mm you'll se that outside in a lot of cases it's pointing downwards but should ideally be facing the brickwork.

On the other hand it could be the expansion vessel, as mentioned check the valve see if water comes out, check the pressure if the pressure is wrong rectify and if works ok for a short while and symptom returns could wellbe the vessel.

[Kevin Wood]

When you say it's going "into the red" does this mean the pressure is too low or too high?

[Sir Tigger KC]

When you say it's going "into the red" does this mean the pressure is too low or too high?

I've assumed that the pressure is too low, hence he needs to keep topping up.