Strange things happening in my header tank.....

[Rallypug]

Hi all

I have a floor mounted Thorn Emi boiler, open flue, vented system which has started doing some strange things. Firstly, when the boiler fires up in the morning, air noises passing through both the boiler and the pump can be heard. This eventually passes through into the rads with me having to bleed the highest rads in the house every other day. The noises from the boiler normally goes away after about 20mins of the boiler operating.
Next, when the system turns off on the time switch (with the boiler still operating) a 'rushing' noise can be heard in the vent and cold water feed lines. I simulated this last night and observed the following in the header tank.... when switched off, the water level in the header tank drops by about 5mm..... when switched back on, the water in the header tank rises by the same amount, being reverse fed by the cold water feed pipe!!.
There was no evidence of any water coming from the vent line into the header tank. Why would the water back feed via the cold water pipe and not through the vent..? Does this mean that I have a restriction in my boiler?
Going back to the boiler, I have progressively over the years had to reduce the temperature on its thermostat due to kettling noises.

I am at the point where I think the boiler is due for a change.
I was going to try and descale and flush.... but am I delaying the inevitable ??

Any advice would be much appreciated before I have to remortgage the house to pay for a new boiler!!

 

[ArtfulBodger]

I have a couple of questions:-

(1) Why have you posted all in bold and enlarged text? is this supposed to attract peoples attention?
(2) Do you really think a boiler costs more than a house?

 

[ricarbo]

If the water level moves a bit it's because the pipes from the tan to the system don't join at exactly the same place and the pump pressure is different at these two places. If it doesn't move much so doesn't cause the cistern to empty or the expansion pipe to discharge into the cistern, it's not a problem.
Continually having to bleed is a problem. could be corrosion gases if you haven't any/enough inhibitor or an air leak inwards through a poor seal somewhere.

 

[Rallypug]

reply to artful bodger .... appologies for posting in large text - i thought it would be easier to read since there was several paragraphs; and no I dont think a boiler is dearer than a house ..... I was being sarcastic!!!

Ricarbo - it isnt a problem with the water level changing - I just want to know if it is pointing to another problem with the boiler... ie is this showing signs of blockage

Ta

 

[Rallypug]

how do i go about finding an inward leak?? (apart from remaking every joint again?)

 

[ricarbo]

An inward leak at a pump - popular because it has washers that could fail - will be shown by removing the pump and observing the colour of the openings at the inlet and exit. If the inlet is brighter, oxygenated air has passed through it.
Elsewhere, you might find a place e.g. radvalve, that leaks when the system is off, but not when the pump is running. Other than that, Gawd knows.
Doesn't sound like a blockage if the water levels go up and down.
If you have to alter the thermostat, perhaps it's 'drifting'. Check with a pipestat etc..
If it's scaled up, try descaling or fernox boiler silencer (good stuff). Cause could be no/too little inhibitor.

 

[Softus]

An inward leak at a pump - popular because it has washers that could fail - will be shown by removing the pump and observing the colour of the openings at the inlet and exit. If the inlet is brighter, oxygenated air has passed through it.

A washer that lets air in but not water out! I've never heard of this ricarbo - do you see it happen often?

Elsewhere, you might find a place e.g. radvalve, that leaks when the system is off, but not when the pump is running. Other than that, Gawd knows.

Er, what? A rad valve that lets air in? A new one on me.

Doesn't sound like a blockage if the water levels go up and down.
If you have to alter the thermostat, perhaps it's 'drifting'. Check with a pipestat etc..
If it's scaled up, try descaling or fernox boiler silencer (good stuff). Cause could be no/too little inhibitor.

I can't imagine why, or how, an open-vented system would scale up.

IMHO, if you have to vent the system every other day, you have either:

1. a rad in a state of advanced corrosion;
or
2. a very sludged up system that is pumping over.

Since you reckon that water does not come up the F&E vent, by elimination you have a corroded system. I would expect that the water that emerges when you vent is quite dirty, and that the downstairs rads take a while to get hot in the bottom centre, and some rads may be rather tepid generally.

There shouldn't be a pressure difference between the vent and the cold feed - if there is then the installation is wrong. However, since you can't see what the water in the vent is doing, you could be seeing the effect of air/gas in the system being compressed when the pump runs.

 

[Slugbabydotcom]

ricarbo wrote:
An inward leak at a pump - popular because it has washers that could fail - will be shown by removing the pump and observing the colour of the openings at the inlet and exit. If the inlet is brighter, oxygenated air has passed through it.

A washer that lets air in but not water out! I've never heard of this ricarbo - do you see it happen often?

ricarbo wrote:
Elsewhere, you might find a place e.g. radvalve, that leaks when the system is off, but not when the pump is running. Other than that, Gawd knows.

Er, what? A rad valve that lets air in? A new one on me.

I've seen both of these phenomena. Very infrequent but they do happen. I only wish I had a photo of the last pump that I saw like this to prove it.

Ever bled a system with the pump running to find air was sucked in due to the air vent being on a negative presure part of the system? Doesnt take too much to figure that a leaking rad valve will suck air in just the same.

 

[Softus]

A washer that lets air in but not water out! I've never heard of this ricarbo - do you see it happen often?

I only wish I had a photo of the last pump that I saw like this to prove it.

So do I. However, if you say you've seen it, then AFAIC you've seen it. I still would like to know if ricarbo has though.

Er, what? A rad valve that lets air in? A new one on me.

Ever bled a system with the pump running to find air was sucked in due to the air vent being on a negative presure part of the system? Doesnt take too much to figure that a leaking rad valve will suck air in just the same.

Well, I'd considered that before making my comment. After all, this is exactly why I never bleed with the pump running. However, "just the same"? I'm not easily convinced of that, because there's a determinable difference in pressure between the position of the vent and the position of the valves. Although, if the rad was at the top of the house, on its own, and higher than the pump? Hmm....

In any case, if I open a vent on a 'negative' (sic.) pressure part of the system, and air goes in, then I turn off the pump with the vent still open, then water comes out. In ricarbo's scenario, water does not come out, which is the nub of my point. Is your scenario the same as ricarbo's, Paul?

 

[ricarbo]

Have to admit, Softus, that I've never seen it myself, on the pump, but have heard of it from others. Seems quite feasible. As to the rad valve, if the gland is leaking a little, it can go unnoticed, and if it's at negative pressure when the pump is running, it won't leak water outwards then. If you stopped the system. water leaking from the valve might be drying off quickly from the hot system, so you still don't notice it. But if the valve is at negative pressure when the pump runs, you can see air could be pulled in.
Rallypug complains of boiler noises, so he might well have a scale problem, he mentions kettling and air in the system and having to reduce his boilerstat.

 

[Rallypug]

Guys

Sorry to start a major debate!!

One further point to add...when I leave the system on 'constant' - say over night - I tend not to get the same amount of air in the system. It appears that when the boiler is left to go cold that air accumulates.

Softus :-

Since you reckon that water does not come up the F&E vent, by elimination you have a corroded system. I would expect that the water that emerges when you vent is quite dirty, and that the downstairs rads take a while to get hot in the bottom centre, and some rads may be rather tepid generally.

Yes the water is dirty when bled (from the nearest rad to the pump- which is also the highest in the system); but the downstairs rads dont seem to have a problem in heating up.

Going back to my original suggestion, should I flush out....?

Many thanks

Andy

 

[Soggy_weetabix]

They are called 'microleaks' and occur regulaly on negative pressure systems.

Tighten all glands on rad valves for starters.

Most common place the air can get drawn in.

 

[bab]

Not to add more fuel to this debate it is very feasable that rad valves with a small weep on the gland spindle can in turn suck air in on open vented systems . Have on quite a few systems found rads that suck air in on the vent when the pumps running. And before u say it i know u dont vent while its running but when refilling a system I allways try all upstairs rads 4 air an hr after its been running . thats when u find it.

 

[Otto Sump]

I have a couple of questions:-

(1) Why have you posted all in bold and enlarged text? is this supposed to attract peoples attention?
(2) Do you really think a boiler costs more than a house?

And your cure is?

 

[croydoncorgi]

Air DOES leak into systems, past washers and especially O rings and dependent on the pressure difference between the water inside and the air outside. So if your (sealed) system pressure is too low, you will definitely get air leaking INTO the higher parts of the system.

Add the effect of the pump, and even more parts of the system will be at negative pressure with respect to atmospheric pressure.

Obviously, the lowest pressure will be at the inlet port of the pump, so this is the first place to look for an air leak.

O rings such as used on radiator valve stems DO NOT WORK EFFECTIVELY if the pressure is low and especially leak air in the INWARD direction. The higher the pressure the tighter the seal.

But if you have a sealed system DO NOT raise the pressure much above 2 Bar. More is not necessarily better.