Potterton Statesman Flowsure - Mystery leak?

[Igorian]

Hi guys

I have a Potterton Statesman Flowsure, which has an unusual leak.

With the CH system up to pressure, 0.8bar, rising to 1.3bar when heating switched on, all appears to work ok. After about 7 - 14 days, the upstairs bathroom radiator is only hot at the bottom, There appears to be no change in pressure. I then bleed this radiator and air is expelled and the pressure drops a little. The radiator is then hot for a couple of weeks and then the cycle repeats until the system pressure drops to zero (after about 3 cycles of the above).

I can find no obvious leak. I would have expected the pressure to drop prior to bleeding if there was one. Can anyone suggest what might be happening?

 

[oilhead]

If the boiler is very hot, you may be making 'air; from The primary water from cavitation at the pump inlet. The pressure only drops when you bleed the radiator, which is to be expected. How long has this been happening?

 

[Igorian]

Hi,

Thanks for the response. I noticed a leak about 6 months ago and saw that the prv was dripping outside. After replacing and refilling, I noticed the current problem.

The boiler is quite hot (too hot to keep hand on the pump for example). The pump is variable speed, and doesn't appear to be an original Potterton one. This was replaced about 5 years ago by someone employed to service the boiler. The setting is currently on 2 (out of 3).

Apart from this issue, it appears to functioning ok. Is this something that can easily be resolved?

 

[oilhead]

Did you check the expansion vessel when changing the prv? If not, it may be worth checking now. Also, when refilling, are you sure the boiler pipework is fuuly bled? The aav on the transfer pipes on this boiler can stick and not work. You could try turning the temperature down on the boiler thermostat to see if it makes a difference, but my guess is that the expansion vessel is faulty. If you depress the Schrader valve in I reckon you'll get water discharge instead of air.

 

[Igorian]

I repressurised the expansion vessel to 0.5bar before refilling. Pressing the Schrader valve releases air, albeit wet (a fine spray). Does this sound like it's had it (i.e., should there be no spray at all)? The system pressure doesn't go higher than 1.3bar when hot, with a cold fill pressure of 0.8bar, so I had assumed the expansion vessel was doing its job.

I had suspected the aav to be faulty, as I couldn't hear any air being released when refilling, but I was careful to full bleed the system at the pump and also using the two bleed valves. I then disconnected power to the burner and ran the system cold to try and move any trapped air before bleeding again. All radiators were bled from bottom to top. I followed the manual for the refilling procedure.

 

[oilhead]

Any airfrom the vessel should be dry. When the pressure is down to nil, is the expansion vessel still full? For a definitive test, disconnect the vessel, set to 1 bar and leave it for a few hours. If it falls in pressure, then it is failed.

 

[Igorian]

The vessel is indeed (slowly) losing pressure, so I've ordered another one (and an aav), which will arrive tomorrow. I'll let you know how it goes.

 

[sooey]

Did you check the shraeder valve wasn't leaking? May just need a new valve core.

 

[Igorian]

Thanks all.

The air was entering via the aav. It sits just before the pump, which probably isn't the best design. I replaced it and no more air in the system.

Once that was sorted, I swapped out the pv too as there was some water in there, but with some compressed air too.

All good.