DIY Doctor

Heating System Boiling

Postby barney130 » Wed Apr 23, 2008 12:29 pm

We have a standard heating system.
(Baxi boiler, Honeywell controls, Indirect cylinder etc)

When we turn either the Hot Water or the Central Heating on, the boiler heats the water for approx. 60 seconds, and then the water boils up through the vent pipe.
Intial thoughts were that the was an airlock somewhere. We drained the sytem fully, twice. We have put mains pressure on the drain off cock at the lowest point but there was not enough pressure to clear the obstruction (if there was one). We have put mains pressure on the boiler, but after a short time, the water was coming up through the vent pipe (with no air gurgling!) and seemed fine.
We have replaced the 3 way valve, hoping that would help, but it did not.
We have checked the air bleed valve and it's working fine.
The pump is definately working.
If anyone have any subsequent ideas, i'd be really grateful.
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Wed Apr 23, 2008 10:21 am


Simply Build It

Postby htg engineer » Wed Apr 23, 2008 3:50 pm

I'd be looking at for a blockage rather than an airlock, will probably be in the flow or return quite near the boiler, probably at a connector or elbow if it's a build up of limescale.

What about the flow and return pipes do they get hot ? does the flow to the cylinder get hot ?

will watch for future posts
htg engineer
Rank: Project Manager
Posts: 3256
Joined: Tue May 22, 2007 5:22 pm

Postby barney130 » Sun May 04, 2008 7:07 pm

Sorry for delay - personal crisis - another one !)

Went to sort it out today - leak from the immersion. Removed immersion, damaged cylinder !!

New cylinder and immersion later.....

When we opened the drain off cock on the boiler, not a lot came out. With the aid of the trusty screwdriver, we managed to shift a blockage and drain it down. Assuming this would sort it, we filled the entire system back up. The system is still boiling after a couple of minutes. The flow on the boiler is hot, and the return is stone cold.

We can only assume its a blockage somewhere in the heat exchanger ?

Does this sound right to you ?
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Wed Apr 23, 2008 10:21 am

Postby Steve the gas » Mon May 05, 2008 5:49 am

2 things to check - is the return valve open- has someone inadvertantly turned it off?
Secondly while boiler is on remove large silver screw on pump to release any air and ensure spindle is turning.Hope this helps
Steve the gas
Rank: Site Agent
Progress to next rank:
Posts: 780
Joined: Sun May 04, 2008 7:07 am

Postby barney130 » Tue May 06, 2008 5:41 pm

Return valve is open, and the pumpis definately working.

We have finally been beaten, and I spoke to a Heating Engineer this morning. He is convinced that it is a blockage and is coming round later in the week to Power Flush the system. This should hopefully clear everything and get us working again. Thank you guys for your help. I'll post later this week as to whether it has worked or not.

If it does, could be worth bearing in mind if you hear of this again in the future.......
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Wed Apr 23, 2008 10:21 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics