System pressure fluctuates between 1 bar (cold) and 1.8 bar (hot)

[philbury]

I have recently had three episodes of my 8 month old Vaillant installed Ecotec832+ losing pressure overnight and being below operating pressure (.3 bar) form a normal pressure the day before. Vaillant have been out to check but find do fault with the expansion vessel or the PRV. There are no apparent leaks in the system which is 13 years old and mostly plastic pipe. The system ran without the need for any secondary expansion vessel the last 13 years with a Glow worm Cxi80. Is it normal for the pressure to go up and down .8 of a bar between hot and cold? Any ideas what's happening?

 

[Scott_D]

How many radiators do you have?

 

[Dom Perkins]

Not sure if all boiler Manufacturers quote that their pressure vessels are there to support the entire system, i maybe wrong, but I think they are only tested to support the boiler 'only'. As another said, how many rads?.. is it a difficult job to cut in a second Expansion vessel to the return?..that being said you are sure you dont have a leak.
it does sound like the pressure vessel is not functioning.. water heats up, expands, pressure vessel doesn't compensate, water goes out the prv.. not the simplest to diagnose

 

[sammathias]

I can only assume valliant have check the expansion vessel pressure... Have you noticed any leaks, staining on ceilings etc...does pipework run under concrete? If you pumped pressure upto 1.5 bar. How soon would it drop below 1 bar?

 

[philbury]

I have 4 radiators and underfloor in one large and one small room. The important part of my post is that there is no steady loss of pressure. It normally goes from 1 cold to 1.8 hot and three times has gone to .3 when cold.

 

[Scott_D]

It must be a leak or an expansion issue

 

[philbury]

Is it normal for a system’s pressure to alter so much between hot and cold? Could it be there is a problem with the pressure sensor????

 

[ShaunCorbs]

Standard normally around 1 bar difference

 

[philbury]

Thanks for all your replies. It has now died 5 times. There are no leaks for sure.It’s still a mystery. Yesterday it went from normal pressure at 1.6 to .3 during the day rather than at night. Could the Vaillant engineer have missed something when testing the expansion vessel and PRV? And could it be a faulty pressure sensor? It repressurises almost instantly with the cocks barely open.

 

[Scott_D]

Any water from the prv pipe outside?

 

[Stigster]

Attach a balloon or the finger from a rubber glove to the end of the discharge pipe if you can easily get to it to see if there is water escaping there.

 

[philbury]

It's completely inaccessible without 3 part ladder and hard to monitor visually because it's above a narrow passage. Maybe Vaillant should put something inline internally to monitor it. It's under warranty but the engineer wouldn't accept that there could be a problem with the boiler itself.

 

[sammathias]

I take it the boiler wont fire up when the pressure has dropped....if thsts the case the pressure sensor is fine. Could be a number of things internally which engineer could check. Sounds like a big leak so you would surely notice if it was pipework related.

 

[philbury]

It's not a pipework leak - pressure is unchanged for days and then suddenly drops and boiler switches off or won't start.

 

[sammathias]

Looks like you will have to get vaillant out again mate.

 

[Scott_D]

Could be a leak that only shows when hot
Best to pay the installer for a few hours to come back and run some tests

 

[philbury]

I'm definitely calling Vaillant out again, I've just been trying to gather info here to counter their previous diagnosis that there was no problem with the boiler or their installation.

 

[Scott_D]

Top up the pressure to 2.5 bar
Turn off boiler
Shut the flow and return valves under boiler
Leave for 24hrs
See if the boiler has lost pressure
Open flow and return valves and see if the system lost pressure

 

[philbury]

Thanks - useful tip.

 

[ShaunCorbs]

In that time don't use the boiler eg heating or hot water

 

[philbury]

I could surprise the family on Christmas Day