New CH boiler Gurgle and air created at 3 port valvr

[Christiane]

Hi
I have had a new boiler installed three months go, it s a Vaillant eco 418, separate water tank initially vented .Randomly massive gurgling sounds traveling through the system appeared .
System was flushed, new pump, new 3 part valve and pressure relief valve.
We changed pump, no change.Then system was converted into a sealed system as suspicion was that air was sucked in by the pump.
No change...Now narrowed it down, it happens at the start of the heating cycle and then totally disappears, unless HW reaches temperature and 3 port valve shuts HW off . No problem, that can be avoided, but the problem at start and finish still exists.
If I switch CH off first and then HW all is well.Unfortunately that doesn't make any difference at start up.
It appears that the water velocity creates masses of air gurgling their way through for about a minute or so.Then all is well all radiators are boiling and the heating is quiet as a mouse
Pump sits in the right place, with flow going right way through.
Tried a system bypass from flow to return before the 3 port valve that made matters worse although it didn't have a valve in so was permanently open
VAILLANT Service engineer and 7 others are scratching their heads...but I have to live with this and it drives me crazy.
3 port valve also has been changed ,that's when we discovered the connection to the HW .
Next suggestion is to insert a valve into the system bypass and check the wiring of the 3 port valve to the timer ....
Any other ideas anyone ? Oh, pressure in system is fine, so no leaks anywhere.
Thank you

 

[45yearsagasman]

Assuming all the air has been vented from your system, and that it's not hydrogen being formed from the system water ( unlikely, but not unheard of ) then it might be cavitation in side the pump. Google that as I'm not going to explain the theory! Bear in mind that air cannot enter a pressurised system when its correctly set up.

 

[Christiane]

Hi, read up on the pump cavitation.The gurgle however does not sit inside the pump but appears to massively start from the flow after the pump when it hits the 3 port valve and then travela through the flow through the system....It a not just a bit of air, it s a MASSIVE gurgle.....gluck gluck....if HW demand is back, immediately all is calm.
Could it have to do with the velocity of the water hitting the valve.
It s not Hydrogen, as it is only on start up/shutdown and when HW thermostat switches off.. In between all is perfect and quiet as a mouse......
Thank you

 

[flameport]

When it was converted to a sealed system, exactly what was done?
What type of hot water cylinder have you got?
What make/model was the previous boiler?
Pictures of the cylinder, pipework, valve, etc. may be helpful.

 

[Christiane]

Hi,
The previous boiler was a Gloworm approx 25 years old.
New boiler installed 3 months ago, sealed 2 months ago via expansion tank.Problem started as soon as it was running with new boiler, but it took us ages to now narrow it down. I will post more pictures when I get home .I also got video but not too sure if I can upload

 

[Christiane]

....can't post video on here but am happy to send if anyone is interested

 

[oph]

After looking at the picture Id suggest that airs being caught around the mid valve. If that was my job id have fitted one an auto air vent on either the a or b ports. I know its being fed from above via the pump id still have done that anyway.

And by the way, did the installer notify the boiler............?#

Theres a reason Ive asked......

 

[oilhead]

God help the person who has to change the 3 port valve head at sometime in the future. Try running the pump on speed 1, and turn down the boiler thermostat. Do you have TRV's? If so, make sure all are open and see if that makes a difference,

 

[Christiane]

Dear oph,

Thank you for the suggestion of an auto air vent .Funnily enough that ( after checking the wiring of timer 3 port valve ) was the next thing in the ' trial and error list ' .
Excuse my ignorance, what do you mean by has the installer notified the boiler?

 

[Christiane]

Dear oilhead,
3 port valve was only changed again 2 weeks ago.
Boiler flow temperature is down to 63 degree. Tried pump on 1, but boiler then sends error message and shuts itself off too hot.
Tried all TRVs open too, no difference.

 

[Nige F]

First (large) picture red head valve at bottom on cylinder return - have it almost shut and see what happens. Next to last picture of pipes and ceiling - auto air vent up high - has the little black cap been loosned?

 

[Christiane]

Hi Nige, Black cap has been loosened , thank you very much.
If return gets closed and water runs solely through the CH that s when it goes loopies.
Same when 3 port valve shuts HW off because desired temperature is reached.

 

[Christiane]

Plumber tried a system bypass between flow and return put with manual valve in case didn't work so we could close.
Well, it failed because the return was then so warm that the boiler didn't think it needed to heat anymore. If manually slowly opened at the start/ shutdown it avoids the gurgle but it then needs to be closed.If left partially open it itself creates that massive gurgle and air , so it is now shut. Potentially automatic bypass valve may be tried but fear is, it may cause the same symptoms.
It appears that somehow the flow / speed of the water hitting the 3 port valve is creating all this.
I am just about so fed up I am happy to rip the whole thing out, despite the £ 2k I paid for it. But fear is, any replacement may do exactly the same if the cause is the design of the pipes......

 

[Nige F]

Auto air vent both sides of the 3 way valve ( belt and braces) and turn the valve so the box is @ the top while you're at it ( not technically necessary but makes changing head easier )

 

[Christiane]

Thanks Nige, funny you should say Auto Air Vent on both sides......it s definitely worth a trial.....my plumber will be busy after the Christmas Break