Blocked PRV on boiler ?

[cholma]

HI, please excuse me if this comes across as a weird question, but boilers, etc., definitely aren't my forte

Got an Alpha SY24. Had a pressure gauge and the PRV replaced about 1 week ago. Found that the expansion vessel is also knackered, and needs replacing. Engineer is coming next weekend to do so. To prevent too much venting, he set the boiler thermostat to 4 so that it cycles down when the gauge gets to around 2.3 (with the CH on). He initally set the cold pressure to 1 bar.

Even with the gauge only reaching 2.3, there was still some water coming out of the PRV, outside. The gauge has gradually falled over the days to around 0.5, although in the last day I haven't noticed any water from the PRV - but I put this mainly down to us only using ther CH very sparingly, given the mild weather here in our part of Sussex.

Probably stupid of me, but to make sure that the boiler didn't cut out due to low pressure (as I may be away for a few days next week, and the wife is even worse than me with the CH), I gently let some water in via the fill loop to get the cold pressure to 0.75 bar.

Had the CH on for a little while earlier, and I'm concerned that there was no venting evident. The gauge got up to around 2.25 max.

Could just be that was only observing venting when the boiler was on longer - but, could the PRV become blocked. Would this require a lot of debris ? I'm hoping that if it is, the fact that the boiler keeps cycling down will prevent any damage to the system.

 

[bengasman]

It's a 3 bar valve

 

[xr4x4]

It's a 3 bar valve

how does that explain that its leaking at 2.3 bar?

 

[mysteryman]

It's because it has been venting excessively due to the failed expansion vessel, and the seating has eroded. You need both items replacing asap.

 

[bengasman]

It's a 3 bar valve

how does that explain that its leaking at 2.3 bar?

Rimes with ducked.

 

[cholma]

Sorry - I didn't make mysself clear in the original post.

The engineer has replaced the PRV, so, it's brand new. He's coming back to add a new expansion vessel (probably next to the boiler) to circumvent the knackered one in the boiler.

The questions are more along the lines of :-

a) when cold pressure was between about 1 bar and 0.65 bar there was still some venting evident with the new PRV, even when the gauge was only maxing at 2.3/4 bar. Could this be because the gauge isn't correctly calibrated, or the internal relief valve is set too low ?

b) regardless of point (a), when I topped up the pressure from 0.5 bar to 0.75 bar, it's now not venting, and the gauge maxes at 2.3/4 still.

So, although the relief valve is behaving now as I'd expect (i.e. no venting below around 3 bar on the gauge), it doesn't appear to be behaving as it was last time the pressure was 0.75 bar. Thus, my concern about possible blockage. I would have thought this is unlikely, given it's a brand new PRV only 5 days old, but ...

Hopefully it's just me being paranoid, or not observing correctly.


One other question. When the boiler has been on, and the gauge has risen, it takes 3-4 hours to gradually drop to it's resting position. Is this normal, or is it a symptom of the knackered vessel ?

 

[WabbitPoo]

TBH why not wait until the guy has finished the job - you'll prob find that it'll be fine then. If its not, ask him why!

 

[bengasman]

A failing prv is invariably due to crap in the system. That meant that when you put a new prv in, chances are that it will fail the first time it activates.

 

[mysteryman]

Assuming that the expansion vessel needs replacing becuase the diaphragm is ruptured, the pressure will rise rapidly as the system water expands - simply because the vessel is u/s. Soon it has to vent through the PRV. The pressure will drop quite a bit as it cools again. Let your man complete his work, and you should be OK.