Boiler Over Pressurising

[b2dan]

Hi

I have a Saunier Duval Thema F23E combi boiler that over pressuries when on. At the minute, it's not heating and is around 0.5bar, however when it's in use, the pressure gauge is at around 3.5bar.

Water then leaks from a valve underneath (The PRV from what I can gather from other websites). Then when the boilers cooled, it can drop below 0.5bar and the low pressure light flashes.

I repressurise this using the ByPass? valve underneath the boiler to around 0.75bar.

If I replace the PRV, will this cure the leak and help to maintain pressure. If so, can it be acheived by a non plumber easily?

Cheers

Dan

 

[adlplumbing]

are u repressurized the boiler if not sounds like a blockage of some sort
stopping water movement then pressure builds up and prv kicks in

 

[b2dan]

I keep re-pressuring the boiler using the filling loop underneath the boiler (it's connected to a braided hose) to 0.75bar, then when I have the heating on it shoots to 3.5bar.

If it is a blockage, wheres this likely to be (radiators?) and how easy is it to find/cure?

I do have a radiator in the spare room turned off, could this cause problems?

Cheers

Dan

 

[Axel]

Sounds like your expansion vessel is either knackered or needs recharging. First thing is to de-pressurise the system, stick a mechanical tyre pressure gauge (the pen type) onto the schrader valve on the expansion vessel (often accessible at the top of the boiler) and measure the pressure. This should be around 0.75 - 1 bar. If it's too low, then pump it up with a bicycle pump till it's at the right pressure.

If that doesn't work, fitting an external additional expansion vessel is what the manufacturer recommends , as the old one is hard to get out without removing boiler.

 

[mike1000]

the expansion vessel on your boiler is flat and needs to be repressurised or has failed and needs to be replaced

 

[b2dan]

Cheers

Thanks very much for the replies.

I'll have a look at things in the morning!

 

[b2dan]

Having a look at the boiler manual and the boiler itself, it seems that the expansion tank is on the back of the boiler on the wall. The schrader valve seems to be on the top of the vessel.

However, the boiler has been set into a recess in the wall and I can't seem to access it! Are there any other ways to access it to test the pressure apart from reaching round the back! (Or am I barking up the wrong tree!)

Cheers

Dan

 

[Axel]

If you can't reach / feel / get access to the schrader valve, then your best bet is to assume that the vessel has lost charge / knackered, and if it can't be re-charged, then you should fit an additional expansion vessel onto the return pipework close to the boiler. They cost about £ 20 from screwfix, and if there is access to the return pipework, then it's a relatively easy plumbing job. I did one on a boiler model same as yours last year and it worked very well after fitting the extra vessel.