Heating system gaining pressure

[spacebiscuit]

I have an ASHP for my domestic heating. I recently drained my system down and removed each radiator to give it a flush and then refilled the system with recommended anti-freeze. I bled and balanced the rads to 1 bar when system was cold and all were nice and hot when heating on.

After a day I noticed the pressure was high - around 2.2 bar, previous to the drain down I would see 1.75bar. So I let some water out of the system to take back down to 1 bar and next day it rose again to around 2.2. Even when cold the system doesn't seem to return to the 1 bar i set it at.

I've checked the valve on the external expansion vessel and when i touch it air comes out and not water - which suggests it is not faulty? If i pull the red cap on the PRV i cna hear water escaping and it re-seats itself.

Any ideas - I'm all out of ideas.

 

[Madrab]

Does the system use a filling loop connected to the mains? If so then that could be passing. Is there a braided hose and is it always connected?

 

[spacebiscuit]

Yes braided filling loop - I've double checked and both valves are definitely closed.

 

[spacebiscuit]

System has been cold for a few hours now and definitely is not dropping pressure - just below 2 bar. I'm reluctantly to drain down again as I have filled iwth anti-freeze - but is there anything I can confirm on the expansion vessel with it in situ - I guess not? It was new only 6 months ago but was there anything I should have calibrated before refilling the system?

 

[terryplumb]

Yes braided filling loop - I've double checked and both valves are definitely closed.

Removing the filling loop would at least rule that out.

 

[Madrab]

It has to be getting pressure from somewhere. Presume it has a HW store/bank, is it unvented?

Only place that would add pressure (if the EV has been ruled out and the pressure still rises when the system is idle) would be the cold mains. So the only 2 places it could be would be the filling loop and HW cylinder coil. As suggested remove the braided hose just to be sure and monitor.

 

[spacebiscuit]

Going to remove the braided filling loop tap now, if the two valves are closed when I loosen the nut it I should not see water right?

 

[Madrab]

Going to remove the braided filling loop tap now, if the two valves are closed when I loosen the nut it I should not see water right?

No, there should be no water. Leave it for a while though - MI/regs state that it shouldn't be left connected anyway - as a passing valve can be a very slow and tiny leak, doesn't take much to increase the system pressure.

 

[spacebiscuit]

I've drained the system down into large buckets so I can re-use the diluted anti-freeze.

I unscrewed the braided pipe from the inlet valve, there isn't water passing until I open the valve. On the other end of braided valve I tried loosen the brass nut and I have water so I didn't continue to loosen it.

System is currently showing 0 bar and the drain down connection has run dry - on the expansion vessel when i connect a gauge to the schrader valve it reads 0.9bar - should I be seeing water when i loosen the brass nut to the hose? if the pressure increases only when the if the pressure increases only when the central heating is/has been running, would this exclude a leaky filling loop?

if the pressure increases only when the central heating is/has been running, would this exclude a leaky filling loop?

I thought the same, pressure went up clearly during heating cycle, when left cold it just sat on 2bar.

 

[terryplumb]

Nero44 ,start your own thread.
System pressure will increase when heating is in use , after heating is not in use and system has cooled down ,the pressure should drop back to what it was.
spacebiscuit ,remove the filling loop and fit blanking caps to both ports.
And then tell us the result.

 

[spacebiscuit]

As mentioned - the expansion vessel was showing 0.9bar on the Schradar valve (with system drained down) so I recharged it to 1.5bar (the value given on the spec of the vessel). I then filled the system to 1 bar, ran 2 heating cycles, one last night and another this morning. Pressure rose to 1.5-1.6 bar and drops back to 1 bar again when cold so now seems stable.

 

[Madrab]

Good stuff.

Just as an addition, if the system is running @ 1 bar then the Expansion vessel(EV) may not need to have that high a pre-charge. The vessel has a factory fill @ 1.5bar but the pre-charge would then be tailored to the system it's protecting. Guidance is normally an EV pre-charge that is at the same or even a little lower than the system set pressure - EV location dependent. That's for a boiler heat source.

Given an ASHP has a lower system temps, I'm not sure how that affects expansion without calcs and the application of the EV pre-charge but I think it would have been fine @ 0.9bar. Too high a pre-charge can also increase the pressure swings during heat cycles as well as one that's too low.

 

[spacebiscuit]

Thanks - good to know. Just a thought - when i initially filled my system I added almost 20 litres of undiluted R600 Sentinel anti-freeze. Is it possible that as it became diluted that it increased by volume and therefore pushed the pressure of system up. When I drained it down yesterday it was diluted - probably half as thin as when it went in.

 

[Madrab]

Looking at the R600 specs I wouldn't suggest that it would increase by volume by being diluted, the only thing I would be thinking about though is that as 20L of R600 provides the min level of protection in a 100L system. If your system is a typical volume and around that, then if the system has had extra water added to it without a corresponding amount of AF then it may have dropped below min levels. There is a test kit that you can get that will confirm if there is enough protection or not.

 

[spacebiscuit]

Yeah i think one of the recommendation was for protection down to a temperature I won't ever see in my location. To put into context I've had no anti-freeze in the system for about 7 years - hence the drain down flush so what I have is 10 fold better than what it was previously with mains water!