• Welcome to PlumbersForums.net - The international free plumbing advice forum. Professional plumbers sharing advice with fellow plumbers and DIY alike. Register for free today! - Checkout the Plumbing Advice forum and then our Plumbing Videos area which still needs populating.

Discuss How long for system to stop requiring radiators to be bled? in the Central Heating Forum area at PlumbersForums.net

colin_

Messages
88
Hi

The system was drained 6 weeks ago as the valves on all radiators were changed in preparation of Evohome being fitted.

I had to bleed the radiators for quite a while after the system was refilled - to be expected.

It is now over 6 weeks and there are still 2 radiators that I am having to bleed daily.

One of these is a radiator that is always open (rest have TRVs controlled by an Evohome) and the other is on the top floor.

There are 18 radiators split over 3 levels.

There is an automatic bleed valve fitted for the unvented hot water cylinder.

Is it normal to still have to bleed some radiators daily?

How long is it expected to be before the system will be free of air and I no longer have to bleed daily?

Thanks
Colin
 

Undertrained

Plumber
Gas Engineer
Messages
1,243
Solutions
2
You shouldn’t be bleeding them for that long after, & no it isn’t normal, maybe a day two. I’d be suspecting a leak somewhere.
 

colin_

Messages
88
Hi

Thanks for the reply.

I was told by the people who did it that it would take several weeks but I am concerned as gone on for so long.

I will ask them back but they are slow to respond as they are busy.

Thanks
Colin
 
Last edited:

colin_

Messages
88
Hi

If it is leaking and the pressure is 1.4 bar on the boiler, would water come out prevent air getting in?

Are there other potential reasons for air getting in as well, if so can you please let me know before I ring them?

Thanks
Colin
 

Chuck

Esteemed
Messages
2,339
It is now over 6 weeks and there are still 2 radiators that I am having to bleed daily.

If you have a significant leak and it's a sealed system it will drop to 0 bar gauge pressure relatively quickly, a couple of days is typical. A system that has been 'disturbed' will usually need trapped air bleeding a couple of times over the first few days and then diminishing amounts of mainly hydrogen due to the (re)formation of a passivating layer for several weeks.

How much gas are you having to bleed out 'daily'? What fraction of the radiators you are bleeding is cold? If the radiator is hot from top to bottom and you are only actually getting a few millilitres of gas with each bleed you are worrying unnecessarily.

Was the system properly dosed with corrosion inhibitor when it was refilled? Was it flushed as part of the process.
 

colin_

Messages
88
Hi

It is a sealed system and it does not drop to zero but does drop slowly (I am presuming that this is due to the air coming out of the radiators when they are bled).

Every day, for the last 6 weeks, 2 of the radiators (+1 occasionally, the rest seem OK) are hot on the top and right hand side but cold on the left hand lower side (about a 1/4-1/5 of the radiator).

To get them back warm and to an even temperature I have had to bleed them every day after the heating has been on in the morning, each one has air coming out for approx. 3-5 seconds every time.

I am not sure about the flushing but I was informed that there was inhibitor added when it was refilled.

Thanks
Colin
 

John.g

Messages
2,793
Probably a good sign in a way that pressure is dropping after venting as it means that no air is being pulled into the system, (unlikely anyhow with a pressurized system). As raw water can contain up to ~ 17% dissolved oxygen then even if all the air has been expelled when filling then a 75 litre system wiil then release ~ 11 litres of air over a period of time depending on boiler water temp and venting arrangements. I often think that shutting off all rads except one upstairs and increasing the boiler flow temp to its max of say 80/85C and then venting this one rad periodically with circ pump off may get rid of the problem quicker than taking weeks at low flow/return temps. Some system though seem to have bigger problems than others and some dont't like temps > 70C for whatever reason. Well installed open vented systems will almost never need venting, after initial rad purging, possibly because of the open vent.?.
 

Chuck

Esteemed
Messages
2,339
Every day, for the last 6 weeks, 2 of the radiators (+1 occasionally, the rest seem OK) are hot on the top and right hand side but cold on the left hand lower side (about a 1/4-1/5 of the radiator).
That's a symptom of an unbalanced system, sediment in the radiator, or poor circulation, not air in the radiators.

To get them back warm and to an even temperature I have had to bleed them every day after the heating has been on in the morning, each one has air coming out for approx. 3-5 seconds every time.
3–5 seconds through a pinhole is very little air. I think it may be a red-herring.
 

hometech

Banned
Messages
162
That's a symptom of an unbalanced system, sediment in the radiator, or poor circulation, not air in the radiators.


3–5 seconds through a pinhole is very little air. I think it may be a red-herring.
AND a result of variable speed pump if you have a system less than 5 years old. Variable speed pumps make the pump curve data meaningless. You can never ever balance a system like this, it will be in a constant state of fluctuation.
 

colin_

Messages
88
Hi

Thanks for all the input.

The radiators get warm evenly when the air is bled out. I am going to continue bleeding it periodically as the colder weather means more radiators that were unused until recently come on. Hopefully after a few more months it will have settled down.

Thanks
Colin
 

Reply to How long for system to stop requiring radiators to be bled? in the Central Heating Forum area at PlumbersForums.net

Similar threads

J
The Boiler/system should have been commissioned properly by the installer but you can check out a few items yourself. System should have been...
Replies
2
Views
284
John.g
J
M
Yeah, I did read this but I’ve inherited the system and the pump looks like it’s been installed since day 1. The radiator in question has got hot...
Replies
8
Views
394
Macka1981
M
C
Hi Thanks for all the replies I think the slow start function of the Worcester is part of the issue I have. I have set it for 20% modulation...
Replies
5
Views
652
colin_
C
B
Just a quick update on the thread. Managed to remove old and install new rads this weekend. All pipes insulated with Bylaw stuff and what a...
Replies
18
Views
843
b21playa
B
C
Thanks for the reply. The ABV is external to the boiler (the Worcester does not have one) and is a run of ~ 50m round trip. The Worcester is...
Replies
5
Views
1K
colin_
C

Newest Threads (Please Reply)

Search Forum

Top