Always Air in system

phester28

My Nans boiler always seemed to always have some air in her upstairs rads even shortly after bleeding them. As part of her aging needs, I moved her timer downstairs and decided that TRV valves on the rads with a service of the boiler was a good idea.

The same plumber has looked after the heating system for a long time.

so 6 rads and a boiler service he was in at 9am and out at 1pm. 360 euro

the next day a lot of noise could be heard from the pipes. he came back and did some work. When I checked with him what he had done he tried to tell me that the immersion was boiling (no element) and that the trv were shutting.

Now I know that the temp of flow away from boiler is not boiling as it does not burn me. so the immersion can not be heated above that temp. I then checked upstairs and found that he also changed the pump, but he could not give me a reason for changing it. (the old one was 1 year old and moving water at a good old rate) the replacement is old and tired looking with only 3 screws in the housing. The air in the system is very noticeable



Long story short the PRV valve appears to be wet most of the time. The autofill loop is always around 2 bar static. I would drop it but the air sound gets worse as the pressure drops. The autofill is turned off (lower knob)

my non plumber guess is that the prv is letting water out and air in. the boiler is at the highest point of the house and so it is always seeing the air in the system. I cant fully explain why the pressure on the autofill never drops off to zero? The charge on the expansion vessel is not zero. I.E I did not have anything to check it's pressure but when depressed for a split second air came out.


The rads don't seem to be filling with air as I have bleed them a few times over the last week to keep a close eye on the system. but the sound of air in the pump is very noticeable especially during the first 1-2 min of operation
Should I get the PRV replaced and maybe an auto air vent fitted?

phester28

Does anyone have any ideas? I dont want to throw good money after bad

rightjob!

is the safety valve letting water out?

if it is it will be causing water to be in the system,get that changed and then if it is an automatic filling loop get that taken out and a normal filling loop installed.

there could be alot of air trapped in the pump aswell,have you tried bleeding the pump?

Dtp1979

phester28 wrote: »

Does anyone have any ideas? I dont want to throw good money after bad

If the prv is passing water then it must be changed. Throw away that auto filling valve. Most importantly, get the pressure checked in the expansion vessel. This can only be done when the system is drained

phester28

As far as I can tell the autofill has a manual shutoff so it is defacto a manual valve.

I will get the prv changed out and check the charge in the next few days.

There is not much room but as the PRV was probably used as drain point would you get a drain fitted at the same time?

Dtp1979

phester28 wrote: »

As far as I can tell the autofill has a manual shutoff so it is defacto a manual valve.

I will get the prv changed out and check the charge in the next few days.

There is not much room but as the PRV was probably used as drain point would you get a drain fitted at the same time?

You might as well because you'll need the system drained to check the vessel and change the prv

Wearb

Dtp1979 wrote: »

You might as well because you'll need the system drained to check the vessel and change the prv

Do you really drain down the system on every service and then replace water and inhibitor each time?

SpaceTime

You can get bubbles of air in a system for a few weeks after a refill due to trapped air, but also due to dissolved gasses in the water.

If you're getting significant amounts of air in a sealed system, it has to come from somewhere, which would suggest there's a leak and air's getting in and water's getting out.

First task is to locate the leak if you can and see if that can be tightened up and resolved.

If that doesn't work and it's a very slow leak, you could try sealants.

A simple addition of an appropriate system sealant might be all that's needed to keep it going. It could just be a weepy joint somewhere.

Just be very careful about using these on systems with microbore plumbing or on certain models of condensing boilers with very narrow tubes in their heat exchangers.

Realistically, you should get a plumber involved but, if it's a very minor leak I wouldn't necessarily go the route of ripping up floors unless you absolutely have to.

SpaceTime

Wearb wrote: »

Do you really drain down the system on every service and then replace water and inhibitor each time?

You probably should if you're not sure what inhibitors have already been used. There's a bit of a risk of a chemical reaction between inhibitors and sealants.

It's better to start on a system that you know just has water in it!

It can be easy enough to block an old system, especially if it's full of debris already.

Regularly draining a system is a very, very bad idea though as you'll just cause rusting of the pipes.
As the water isn't changed, it eventually becomes saturated with metal ions from the plumbing and won't absorb anymore. It will also contain oxygen and chlorine which will react with the plumbing a little. If you put in clean water, it will dissolve out the pipes until it reaches a balance. That's why you need inhibitors.

If you keep putting in fresh water either due to topping up a leak, or by regularly flushing out and refilling the system, you'll end up with leaks and rusty radiators in no time.

Also, if you're in a hard water area, you can cause serious problems with deposits on the heat exchanger of the boiler and elsewhere in the system if you keep adding more limey water.

Dtp1979

Wearb wrote: »

Do you really drain down the system on every service and then replace water and inhibitor each time?

Not always no, but if the vessel needs charging then you have to.

Wearb

Don't mean to harp on, but if you can test its charge with water in the system, then you can charge it with water in the system.

Anyway we have travelled this road in these threads before. I don't drain down. I just let off the pressure for a near enough reading I only do this if I find signs of a problem. Like a prv letting water by, or pressure really low. Then I lower it to zero and even let more water off if the vessel is higher than the gauge. Then I check vessel pressure. It will be empty of water after doing the above.

Dtp1979

Wearb wrote: »

Don't mean to harp on, but if you can test its charge with water in the system, then you can charge it with water in the system.

Anyway we have travelled this road in these threads before. I don't drain down. I just let off the pressure for a near enough reading I only do this if I find signs of a problem. Like a prv letting water by, or pressure really low. Then I lower it to zero and even let more water off if the vessel is higher than the gauge. Then I check vessel pressure. It will be empty of water after doing the above.

To be honest I'm mostly talking about gas boilers. So it's easy to isolate the boiler and vessel and drain.