worcester bosch highflow 400 combi - falling pressure

[beth]

About 3 weeks ago I noticed that my combi pressure was falling to under 1bar when system off. Usually sits about 1.5bars when asleep. I topped it up and began to search for leaks over the next few days, but could not find any, and suspected it was a leak under the floor. The boiler is about 4 years old and up until now I have not had any problems except sometimes if someone runs a bath, the system trips and needs reset, although this happens very infrequently.

Anyway, I thought I would leave the system and monitor the loss in pressure over the holiday period as I still had hot water and heating. When the system had been running for about 3 hours I checked the pressure and it was about 3.5bars on the gauge which I thought was a bit excessive. I wondered if the PRV was actually working, so operated it manually and water was released and the pressure fell rapidly.

It took a few days for water to stop dripping from the PRV outlet and the system now sits at under 1bar when off and reaches about 2bars when running.

I am now contemplating calling in the Gas board to check the system for either a fault or a leak but do not want to waste their time if at this stage the problem would be too difficult to diagnose.

I would appreciate advice on the best way forward.

 

[oilman]

Leave it alone. There is no problem. The pressure will be less when it's cold than when it's hot. I would set the pressure to 0.8 bar cold, and you should see it rise to below 1.5 bar when hot. If it rises to more than this, the expansion vessel is either faulty, or is too small for the system.

The PRV and the expansion vessel should be checked at every service. If the service guy doesn't do it, find someone else who does.

 

[COG]

As oil man said if it does not exceed the two bar on avv then its ok if your prv is simply dripping then it will have to be cleaned out or replaced. If you want to simply check your pressure vess the undo the one screw holding it abd lower it on its hinge if weighs more than 20lb its had it,its on a good flexi line so you cant damage anything,you have to lower it down to service the boiler so its a fairly easy one to spot.

 

[beth]

oilman and COG, thanks for the advice.

The boiler installer had set the red arrow on the gauge to 1.5bars
and told me at the time that this was the minimum pressure
required, so I always thought this was right. This was 4 years ago.

Do you think any damage could have been done due the system
hitting 3.5bars ?

 

[COG]

As long as the prv is not passing it should be ok ,its tested upto 10 bar at the factory.