Gurgling boiler + Air in CH + FE tank

[spatel]

Final say before "D" day tomorrow, IMO that lever valve is a balancing valve on the hot water coil, to give a reasonable cylinder warm up time but divert as much water as possible to the CH when both systems are calling for heat. They are often fitted in the form of a gate valve on the return of the coil and were always fitted in systems with no zoning.

Thanks John!
In terms of plumber #2 tomorrow.
Just wondering how to strategically unload the info to him and how he should investigate in what order.
1. Boiler (whooping noise)
2. Look at piping system around boiler (determine what goes where)
3. Trickling noise from the Rads
4. Air in system
5. Blocked pump
6. Blocked cold feed
7. Condense vent block
8. f+E tank levels
9. Cold water tank feed

Sounds reasonable? Thanks!

 

[John.g]

1A. Boiler heat exchanger blocked.

 

[spatel]

1A. Boiler heat exchanger blocked.

Thanks!

 

[John.g]

Hope you are sorted, there is a very interesting thread here of a few months ago "Air problem in open vented system after boiler change"

 

[spatel]

Hope you are sorted, there is a very interesting thread here of a few months ago "Air problem in open vented system after boiler change"

Thanks John for asking but no unfortunately not. Plumber #2 was a nice chap with clear experience and knowledge but said that the fault could be at one or many places! So none the wiser unfortunately.
One thing he did say was that it would be good to rule out a leak that could be the root of the problem. Suggested that to tie of the ball cock of F+E tank, mark the level and the see where it is a few days time. Use immersion water during that time. If it isn't a leak, he suggested that there could be a block of cold feed (green piping in my diagram) just above the boiler (I think you called it the top up). He seemed to think that of there was a block it would be there. So he said to cut the pipe above the M.filter and the top, and clean/replace that bit. Alternatively, to try a magna flush piping kit to get rid of any crud. The other things he said was a noise reducer for the boiler, an air vent valve near the motorised valve close to the lever of the HWC. Finally to consider making it a sealed system. So lots of ideas but of course, its hard to know which step to take! I did ask about the heat exchanger and he said that it could be but then you might as well change it all!
Whilst he was here he did notice the trickling noise in the rad closest to the boiler and said could be pieces of debris stuck. Then he saw the new TRV on it and when he took it off and pressed on the pin, it started hammering and said that was not right.
So will need to see what can be done about that!
In any case, I shall read the thread you mentioned as it sound a similar story to mine (hopefully with a favourable outcome!!). Thanks for your help John!

 

[John.g]

Re possible blockage of cold (green) feed at boiler, if you feel this as high up as you can it may be warm as you did see bubbling in the F&E tank.
No simple answer then. Could you run the circ pump for a extended period (would need separate supply) with boiler off and see if noise persists.

 

[spatel]

Re possible blockage of cold (green) feed at boiler, if you feel this as high up as you can it may be warm as you did see bubbling in the F&E tank.
No simple answer then. Could you run the circ pump for a extended period (would need separate supply) with boiler off and see if noise persists.

How could one one run a pump without the boiler on?
Also, I have noticed that when the pump turns off whether on with CH or HW, the water levels go down quite significantly in the F+E tank. When the system is turned on again, water levels start to rise.

 

[John.g]

The wiring would have be removed in the pump terminal box and a live supply wired in there, before doing this the MVs should be manually opened with the lever(s) on the side(s).
The water level falling in the F&E tank (whatever the reason) would indicate that the cold feed isn't blocked as that is the only connection to the system apart from the vent. Can you tie up the ball cock as suggested by the plumber and see if the level changes over say 24 hrs, checked when system is cold, maybe first thing in the morning.

 

[spatel]

The wiring would have be removed in the pump terminal box and a live supply wired in there, before doing this the MVs should be manually opened with the lever(s) on the side(s).
The water level falling in the F&E tank (whatever the reason) would indicate that the cold feed isn't blocked as that is the only connection to the system apart from the vent. Can you tie up the ball cock as suggested by the plumber and see if the level changes over say 24 hrs, checked when system is cold, maybe first thing in the morning.

I think the wiring of the pump is beyond my remit.
Yes. I will try out the ball cock trick this weekend. Would the receding of water from F+E tank when the pump is off is because the water is replacing the air and then when turned on again the water rises?

 

[John.g]

The rise and fall of water in the F&E tank could be caused by either a imbalance in the cold feed line and the vent or it could be caused by the air expanding in the system when it heats up and displaces the water, it would require ~ 5 litres of entrapped air (quite alot) when heated to 70C to displace ~ 1 litre of water. If the level in the C&F tank falls almost immediately on the pump starting then IMO its the former is the cause. If you check the level on boiler start up you can verify this or checking the level from a fully hot system when the pump stops.

At the end of the day all the theorizing in the world won't solve the problem, some will contend that the only real fix is to install a sealed system, if indeed that will fix it.
One compromise is the combined feed&expansion, it might/may work and only entails the emptying the F&E tank (ball cock tied up) and then drain off a litre or two and tee the cold feed directly into the vent as both are on the same left hand side of the tank, then blank off the "old" cold feed at the top, it can always be blanked permanently at the boiler at a later date if successful, it should only take a few hours.

 

[John.g]

Should have asked before, what is the boiler set point temperature? and have you tried running at say its minimum to see does it have any affect on the noise?.

 

[spatel]

Should have asked before, what is the boiler set point temperature? and have you tried running at say its minimum to see does it have any affect on the noise?.

Thanks for the suggestion John of Teeing off the vent and cold feed. I will check this out. I did read the thread you had kindly suggested but am unsure if they ever solved their issue (which involved a much larger level of change to the system than I have). The boiler set point temperature is a gauge and not numbered. Initially it has been on quite high and I have turned it done significantly. Can't say I see any improvement to the system tbh. The short cycling still exists, air sound still trickling somewhere in the pipes and poor performance in some of the rads. I will try to set to minimum tonight. Its getting to a point where I can't see this being ever resolved but I shall persevere before considering a sealed system. I' m not inclined yet to go down this road until I am absolutely convinced that my piping will be able to withstand it. Thanks!

 

[John.g]

That thread was very interesting in that the system is fine at 65C but not at 70C, that was converted to a combined feed & expansion and it still did not solve the problem so maybe be a waste of time in your case, a leaking boiler HX was/is? the main suspect there I think.

If it (yours) was my system, I would, in view of old pipework etc, convert it to a semi sealed system, it would only entail installing a AAV on the removed vent, fitting a swing check NRV in the feed and installing a 12 litre E.vessel teed in just before the circ pump. You already will have a static system head of ~ 0.5 bar, on conversion to the above system, a 12 litre E.vessel with a pre pressure of 0.5 bar, will only rise to ~ 0.75 bar with hot system and that certainly won't pose any pipework problems.
Sealing the system and installing the E.vessel before the circ pump will almost guarantee no ingress of air, then just get rid of the entrained air.
Would also suggest removing the pump head and checking for any blockages in pump ports and the impeller, this can be done at anytime by just shutting the pump isolation valves and removing the pump head.

I was looking at the Main HE boiler manual today and it states that it has a pump overrun of 2 mins which implies that there is, or should have been, a ABV (automatic bypass valve) installed somewhere on the system, have you got one of these?, it will be fitted between the flow & return probably fairly close to the boiler, if this is fitted and is not set up properly or malfunctioning then it will cause all sort of problems as you could be short circuiting the CW/HW systems, have a good look around for this.

 

[spatel]

That thread was very interesting in that the system is fine at 65C but not at 70C, that was converted to a combined feed & expansion and it still did not solve the problem so maybe be a waste of time in your case, a leaking boiler HX was/is? the main suspect there I think.

If it (yours) was my system, I would, in view of old pipework etc, convert it to a semi sealed system, it would only entail installing a AAV on the removed vent, fitting a swing check NRV in the feed and installing a 12 litre E.vessel teed in just before the circ pump. You already will have a static system head of ~ 0.5 bar, on conversion to the above system, a 12 litre E.vessel with a pre pressure of 0.5 bar, will only rise to ~ 0.75 bar with hot system and that certainly won't pose any pipework problems.
Sealing the system and installing the E.vessel before the circ pump will almost guarantee no ingress of air, then just get rid of the entrained air.
Would also suggest removing the pump head and checking for any blockages in pump ports and the impeller, this can be done at anytime by just shutting the pump isolation valves and removing the pump head.

I was looking at the Main HE boiler manual today and it states that it has a pump overrun of 2 mins which implies that there is, or should have been, a ABV (automatic bypass valve) installed somewhere on the system, have you got one of these?, it will be fitted between the flow & return probably fairly close to the boiler, if this is fitted and is not set up properly or malfunctioning then it will cause all sort of problems as you could be short circuiting the CW/HW systems, have a good look around for this.

Thanks John, I appreciate your advice and details for the conversion. I really just find it a little bit disheartening that it would need to go down this road when clearly the system has been in good operations for the last 4oyrs and that one set of minor work has created this imbalance!
In term of the ABV, I can't seem to see one. But from the reading online, this could be highly relevant given that TRV's have now been installed on all but one of the rads downstairs (only 2 out of 9 rads had TRVs previously, now 8 of them do). All the rads upstairs have got TRVs and not been touched. Based on this TRV, would you think that installing a ABV should be installed? and would you think that installation of a TRV on the wrong side of the rad is not good (as I think this might be the case of the kitchen rad closest to the boiler? -doesn't see to be a bidirectional one ---can't see arrows). Thanks!

 

[spatel]

I was also looking at the boiler manual just now and it mentions that existing alternative bypass is possible.
In my case, I noticed that when the HW is on, the bathroom rad and the towel railings do heat up. The Towel rail has 2 lockshields whilst the bathroom is fitted with a TRV on one side. Does this seem right to you in that this might be the alternative to the ABV?

 

[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?.