Rivers in Pipes!

[justino]

I hope I can get some help with a problem I have created with my central heating/hot water system.

First off it is a sealed system, 3 way valve, with Hot water cylinder, and Ideal Standard Elan 2 boiler. The boiler is on the ground floor, the HWC is in the attic (3[SUP]rd[/SUP] floor). All was working fine until about 3 weeks ago. I replaced a bottle air vent by the HWC that was weeping slightly from the top. To do this I released the pressure from the expansion vessel until it was reading zero, then replaced the bottle valve, then refilled the system, bleeding the top 2 radiators in the attic as I refilled. I then turned on the hot water to allow the system to circulate.

I came back 10 minutes later to find the pump red hot, input pipe hot, and the outlet cold. I can’t remember how I got it flowing, I think turning on and off a few times, but eventually the outlet got hot, showing the pump was working. I recall it went cool a couple of times before it settled down. The pump is a newish Alpha 2. However I now have what sounds like rivers running through the pipes, ie air. Its worse when on the hot water only. No amount of bleeding the radiators and the new AAV makes any difference. You can hear at the pump, in the pipes and the 3 way valve upstairs.

Thinking the air lock running of the pump may have damaged it, I have fitted another pump, which initially whilst the system was cold sounded quieter, but once up to to temp, the noise came back.

Having done some research thought it may have been sucking air in on the inlet side of the pump as a result of the 10/15 mins of running whilst air locked, so I replaced the olive (28mm) on the pump valve. This made little difference.

I have now run out of ideas. The system is holding pressure, and the expansion vessel has air in, although I have not checked the pressure yet. The system was fine before this, running completely quiet on speed 3, but now even on speed 1 I have rivers running through the pipes. The boiler will lockout if left on speed 1. I have minimised the noise a little by increasing the pressure to 2.5 bar when warm, but its still there.

Could the constant suction created by the pump have created a source for air to be sucked in elsewhere, eg inside the boiler or elsewhere. Any ideas appreciated.

Thanks

Justin

 

[Reg Man]

Air trapped in the system. The new auto air vent may not be working.

 

[justino]

No, definitely working, as when I release the plastic cap, the air that has risen is released. I have now left the cap undone so when any air rises it can find its own way out.

 

[justino]

Seems to be getting worse now, must be drawing air in somewhere, but where? I don't think it is the same amount of air constantly going round as some finds its way into radiators, or out of the AAV. Driving me mad. What damage could the pump running for 10-15 mins whilst air locked have caused elsewhere?

 

[stevetheplumber]

the only place a sealed sytem can draw air in is through the aav you said you vented the top rads did you vent all rads?

 

[justino]

Been a bit busy with work, so not had much time to investigate further. What I have noticed is that the problem only occurs now on the hot water setting, and is perfectly quiet when on heating only. My theory is either the air that is being drawn in is going into the radiators, and being released through the Aladdin AAV the top two rads have, therefore not circulating, but doubtful as you'd hear it circulating in part of the system, or air is being drawn in somewhere on the HW only part of circuit, which is the HWC, HW side of the 3 port valve, couple of gate valves and the AAV as stevetheplumber mentions. So I think I will investigate that further this weekend.

 

[CXR100]

dont know why people bother with aav, stick a 5 inch piece of 15mm up from a tee and solder a manual one on instead! air will find its way up that 5 inch piece and get trapped there! release it every so often! much less hastle, and anyway arnt aav,s only suppose to be left open whilst commisioning by some M.I's???????

 

[lame plumber]

try bleeding the pump the next time its replaced!

 

[justino]

I am making progress. I have been checking all the compression fittings on the AAV, 3 port valve etc and noticed an improvement, however it was probably from reducing the pressure in the system (after I had increased it to help reduce the noise) and the PRV reseating better after being opened and some crud preventing a good seal. On realising this I recalled the flagstone under the pipe outside had been damp, ie it was leaking slightly, so was probably drawing air in also.

For the time being, I have flushed the PRV by opening it, and at the same time turning on the filling loop which would flush it. Doing this has improved the situation no end, with just the occasional 'fizziness' heard and odd glug now and again, usually on turn on of the hot water. After Christmas I will drain down, and flush the PRV more thoroughly or replace as I highly suspect this is the cause.

Lesson learnt - do not use the PRV as a way to partially drain down, and fit a magna clean or similar to filter the crud out.