Water dripping/running inside hot water tank - why?

[alba2]

I am coming at this again because thus far no diagnosis.

I have an unvented system powered by Ideal Classic FF250. The hot water tank is a Tribune Premier.

When the pump is running there is a constant dripping and frequent significant continuous running water sound from inside the tank. It sounds like water dropping onto water. When the system is off and the pump off there is no sound from the tank.
The ch and hw system is fully functioning, with plenty of heat.

I have drained down and refilled the system and topped up with inhibitor.
Re pressurised the CH expansion vessel to 0.5 bar.
The h.w. expansion vessel is at approx 3.5 bar.
The c.h. expansion vessel sits constantly at 1.5 bar
Checked no water coming through tundish.
Checked no water coming from the 2 outside outlet pipes.
Bled the radiators.
Bled the pump.
Opened and checked that the TR22 valve is working by expelling water.
There are no leaks anywhere.
The refill loop is closed.
There was no running water sound before the ch expansion vessel had the schroeder valve replaced and repressurised etc.
What seems to be the problem and what else can I do to check the system?

I am probably wrong but the only conclusion I can come to is - could it be an air build up at the top of the tank so the sound is water dripping onto a lower surface water level? If so how can this air be removed and the hw tank fully topped up with water?

 

[Schvink]

Hi there,
With it being an unvented cylinder the only way that air would be released from the top of the tank is through a tap. Because an unvented system is normally pressurised up to 3bar, you would get enough pressure to force air through a hot tap. I've read carefully what you wrote, and i cant think of anything more it could be other than maybe air with in the coil. It's evident the coil may not be split as the water in the U/C is great than the C/H, thus would cause the pressure in the CH to rise. Is there an AAV (auto air vent) on the flow of the coil to the cylinder?

 

[alba2]

Hi there,
With it being an unvented cylinder the only way that air would be released from the top of the tank is through a tap. Because an unvented system is normally pressurised up to 3bar, you would get enough pressure to force air through a hot tap. I've read carefully what you wrote, and i cant think of anything more it could be other than maybe air with in the coil. It's evident the coil may not be split as the water in the U/C is great than the C/H, thus would cause the pressure in the CH to rise. Is there an AAV (auto air vent) on the flow of the coil to the cylinder?

Thanks for trying to help.

The primary flow and primary return on top of the Tribune Premier are each Teed off vertically, and end in small knurled cap/valve? They are both a little gunged up.

As I said there is no water dripping in the tundish until I open both relief valves to test that they are working. Both relief valves work fine and water is temporarily discharged.

I just can't get to the bottom of this. Both ch and hw are heating fine. Yet when the system is on and up to temperature and no water is being run I get this plop plop plop constantly which sounds like water dropping into a tank of water. It does not stop until the late evening when the system is switched off completely.

The sound changes to one of constant running water like a tap running inside the tank when we run a hot water tap or the shower. It continues for quite some time afterwards. I assume that this is the pump circulating water through the coil in the re-heat process, but it is really quite noisy, and I was never aware of both the constant dripping and running tap noise before.

Are both the above noises normal?

Would air within the coil cause this, and if so how do I rectify it?

 

[Agile]

You seem to be assuming the noise is HW inside the tank.

But if it was then it would not stop when you turn off your boiler.

We think it is air in the heating coil.

The knurled caps are manual air vents! Does water come out of them if opened a turn or so?

If they are blocked then they can be unblocked with a needle but only do it with system cold and prepare to get wet.

Tony

 

[alba2]

You seem to be assuming the noise is HW inside the tank.

But if it was then it would not stop when you turn off your boiler.

We think it is air in the heating coil.

The knurled caps are manual air vents! Does water come out of them if opened a turn or so?

If they are blocked then they can be unblocked with a needle but only do it with system cold and prepare to get wet.

Tony

Tony. thanks for your help.

Yes as they are so small they look like manual air vents. One is knurled and the other has a slotted head.

Would air in the coil cause the problem I have been describing and if so would opening these manual air vents bleed the coil and cure the problem?

I am going to spray them with WD 40 then clean them up before attempting to open them.

Apart from letting the system cool down, do I also need to depressurise the system? Do I also need to completely switch off the system so the pump is definitely not working?

 

[alba2]

Good news Schvink and Tony, your advice has fixed the problem. Once again thanks for your help.

I had been wrestling with it for about a week.

Now that the problem has been fixed could you please assist with 3 supplementary questions?

After draining down the system to fix the faulty schroeder valve I dosed the system with plenty of inhibitor before filling up. However because of this problem I drained the system down again via the pressure relief valve and refilled. (I know your not supposed to do this. I usually do it through the lowest drain point!) I am under the impression that not so much water is drained down this way, so am wondering do I have to add inhibitor again?

Should I replace the 2 manual air vents with automatic ones if I drain down for any reason in the future?

Trying to find a solution to the problem I turned the speed of the pump down from the number 2 setting to number 1 (3 settings on Wilo Gold 50). The ch & hw system seems to be working fine at 1. Should I return it to its original setting of 2?

Thanks

 

[Schvink]

Excellent. Glad we could help. in response to the 3 questions:- 1) The amount of water drained would depend on where your PRV is situated. No water below that PRV would be able to drain out. Also if you didnt opn any vents on the rads or introduce any air to the system while using PRV then more than likely just the pipework was drained. As a simple rule of thumb I use the method of "for every radiator use 0.1L of inhibitor." I.e 10rads=1L so on and so on. So it really depends on the litres of water that was drained. Be weary of over inhibition as that has been known to cause issues aswell. If you are really unsure, drain the lot and start again.
2) AAV'S are good. Clue would be in the name, it automatically vents air. They do sometimes fail and leak. Its a pros and cons sort of weigh up considering you have manual vents. I would say its up to you.
3) If your system was set on 1 previously and worked fine then I'd say put that back to 1, it was most likely balanced to that setting. Plus a pump set too high can generate air on smaller systems. (Worth keeping in mind)

 

[Schvink]

Sorry meant setting 2 for pump.

 

[alba2]

Many thanks again