Gurgling boiler + Air in CH + FE tank

[John.g]

It the noise is still there with all TRVs fully opened up to index 5 or whatever then the problem is elsewhere.
IF the HW MV (zone) supplies the towel rad then they still won't act as a bypass on boiler, because once the HW is satisfied then the MV will close and there is nowhere for the water to go, ditto for the CH, hence need for dedicated ABV, but if it was never fitted then why should a noise problem arise now?.
I would suggest the you yourself remove all the TRV's heads, reduce the boiler stat to minimum which is 62C (range according to manual is 62C to 83C)

Maybe get plumber1 or someone competent to do so and remove the wiring from the pump terminal box and run a temporary supply from a extension lead or whatever, open the MV manual levers and run the pump with boiler off and see if noise still there with "cold water".
Also get him to remove the pump and check for blockages as I've said before a number of times. I think you will have to get plumber1 re involved and take it one step at the time.

 

[John.g]

If the towel rail hasn't been piped independently of both the HW& CH MVs and if the the pump overruns for two minutes then IMO it is very likely going to push water up through the cold feed and pull air in through the vent as the pump head will be at its highest for this two minute period, of course if nothing has changed in the past few years then this should have been happening as well.
The pump overrun may not be used, very easy to check out, fire up the boiler using only one zone and then after a few minutes shut off the zone to shut down the boiler and feel or listen to the circ pump to see if it continues to run for another 2 minutes.

 

[spatel]

If the towel rail hasn't been piped independently of both the HW& CH MVs and if the the pump overruns for two minutes then IMO it is very likely going to push water up through the cold feed and pull air in through the vent as the pump head will be at its highest for this two minute period, of course if nothing has changed in the past few years then this should have been happening as well.
The pump overrun may not be used, very easy to check out, fire up the boiler using only one zone and then after a few minutes shut off the zone to shut down the boiler and feel or listen to the circ pump to see if it continues to run for another 2 minutes.

Thanks John. I will try to get plumber 1 involved again if he is willing and test the various things you recommended one by one. I tried to remove the TRVs today but some of them are fixed so tightly that I can't remove them off by hand! Placing the boiler temp to minimum still results in short cycling of the boiler. The rads are still blazing hot even at minimum setting. If you hadn't have lived so far away I for sure would have invited you here to look through the system!

 

[spatel]

Hi John,
Just to comment on the pump overrun and to double check with you. No matter whether I turn on the CH or HW, the boiler does fire up. The gurgling noise is most apparent with the HW switched on. When I turn off either the CH or HW, the boiler switches off and the pump continues to run for about 2 minutes. When the pump finally turns off, you then hear the swooshing water sound escalating up the magnafilter and return pipe.
So, yes the pump does overrun with either zones.

 

[John.g]

Very good, have you checked for pump overrun when boiler shuts down?
Just saw your post there now will comment in a few minutes.

 

[spatel]

Very good, have you checked for pump overrun when boiler shuts down?
Just saw your post there now will comment in a few minutes.

Yes, pump overuns when boiler shuts down whether switched off manually or timer using either CH or HW systems

 

[spatel]

I am just wondering that since the installation of the all the newTRVs that the ABV is now necessary but was not needed before?

 

[John.g]

I can't see why they should make any difference because when the boiler shuts down, the residual heat in theHX has to go somewhere, if no bypass, either in the form of utilizing a towel rad, (piped in downstream of both MVs) or a ABV, then the water temperature will rise to a very high level especially in your type of boiler which is non modulating?. Oil fired boilers are ALL non modulating but the boiler contents are X10 times that of a gas boiler, my 20kw oil fired boiler contains 20 litres of water with no overrun/ABV but that 20 litres acts as a buffer to absorb the residual heat, I have measured the temp increase at 10/12C, if it had contents of only say 2 litres then that temp rise would theoretically be > 100C. so you can see why you may get a lot of strange sounds on shutdown.
Some gas boilers have SS HXs and don't require a ABV but I would venture that most if not all of these will have a sealed system where the temp rise is accomodated by a slight increase in pressure in the E.vessel and the SS material isn't affected by that temperature rise.

Food for thought, but can you do one final test now, with say the CH zone only on and boiler firing, shut down the boiler but immediately open the (CH) MV with its manual lever and keep it open for that 2 min overrun and see does it make any difference to those noise levels.

 

[John.g]

But yes, in answer to whether a ABV should be fitted where no towel/rad bypass then from you manual...

"Systems with Thermostatic Radiator Valves (TRV’s)
Where mechanically operated thermostatic control
valves are used, the total length of the by-pass circuit
taken from the boiler connections should be greater
than 2 metres of 22 mm pipe. The bypass should be
capable of maintaining a minimum flow through the
boiler of 9.0 litres/min (2 gal/min)."

 

[spatel]

But yes, in answer to whether a ABV should be fitted where no towel/rad bypass then from you manual...

"Systems with Thermostatic Radiator Valves (TRV’s)
Where mechanically operated thermostatic control
valves are used, the total length of the by-pass circuit
taken from the boiler connections should be greater
than 2 metres of 22 mm pipe. The bypass should be
capable of maintaining a minimum flow through the
boiler of 9.0 litres/min (2 gal/min)."

Thanks for the information. I just ran your test. Interestingly,when I put on the CH system and left the (CH) MV in its normal or manually open position after switching off the boiler, I didn't actually here the swooshing or gurgling noise at all.
BUT, on the HW system there is the swooshing sound in the normal CH(MV) setting. When I manually keep open the CH (MV), the swooshing sound and gurgling sound is less apparent.
So to me, it seems related to the HW system. The short cycling is very apparent with HW (every 30s) and much less so with CH (though it still happens).
Thanks!

 

[John.g]

In normal circumstances the CH system will require a much higher input than the HW, when the hot water cylinder is cold then the coil may absorb 10 Kw but as water temperature approaches 60C then the coil may only be absorbing ~ 2 kw hence more cycling but every 30 secs is certainly not normal, one might expect ~ 3 to 5 mins. It could point to a lime scaled coil if you live in a hard water area or a very poor circulation rate through the coil for whatever reason.

What is your boiler output?.