DIY Doctor

Advice Needed as No Hot Water Flow From Glowworm Flexicom Boiler

Postby steve12345 » Mon Jul 18, 2016 1:51 pm

About me: non-professional, average DIY guy. new to this forum.
My boiler: Glowworm Flexicom24cx combi

Long story short, yesterday I set about removing a sink and radiator from a bathroom that's soon to be renovated. I turned off the mains water at the stop-cock, as well as ensuring the heating wouldn't kick in.
Completed the job, turned stop-cock tap back on and checked for leaks – all good!
I noticed the boiler was reporting it had very low pressure so I topped it up to 1 bar with the filling loop hose.

End result:
Central heating – fires up and radiators work fine
Cold taps – good pressure works fine
Hot taps – very low pressure, flow quickly falls to a dribble then stop. Boiler doesn’t fire up on demand as it should.

I then noticed that the boiler pressure was increasing ever so slowly, 1.1 bar, 1.5, 2.0, and now settled on 3.5 bar after a few hours.

I suspect what's happened is I had the sink taps (hot & cold) open when I turned off the mains water suppy and stupidly didn’t turn the boiler off at the mains. So it might have been trying to supply hot water when there was no cold coming in and this has broken something.
No error messages or funny smells though.
The increasing pressure in the CH system might be down to either me opening up the stop-cock more than it was originally, or possibly not turning off the filling loop hose fully.

So in short, low pressure in hot water, high pressure in CH.

Can anyone offer any advice or opinions as to what might be the cause or things to check for?

So far I'm guessing...
a) burnt out pump for the on-demand hot water system
b) accidentally fiddled with a valve setting on a pipe into the boiler when using the filling hose
c) incorrectly drained and refilled the system resulting in trapped air or broken sensors

Many thanks, and yes I shouldn't be allowed near any plumbing again!
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Mon Jul 18, 2016 1:15 pm


Simply Build It

Postby lets have a look » Tue Jul 19, 2016 5:16 am

could be the heat exchanger,diverter valve,sensor,do you have low hot water pressure in the kitchen
lets have a look
Rank: Foreman
Progress to next rank:
Posts: 213
Joined: Sun Mar 20, 2016 7:59 am

Postby steve12345 » Thu Jul 21, 2016 10:29 am


Thanks for your reply, it's now better but not perfect.

* I reduced the high boiler pressure back down to 1.5 bar by bleeding a radiator

* Checked the filling loop taps, one was very stiff to turn which made me think it was closed when it was not. This is now shut off properly resulting in a stable boiler pressure and less water being stolen from the hot water supply. Not sure why both need to be off though, surely just one closed tap is enough?

* The inline tap on the cold supply for the DHW was not fully open, doing this has now increased the flow enough for the boiler to recognise a demand and to start heating

* The hot flow is still poor compared to cold, but sort of working ok for now. I've only just moved in to the house so can't remember what the flow was like before, it might have been the same. Plan is to redesign the kitchen soon anyway so will need to reposition the boiler and get a professional to recheck all this.

One final thing. I'm wondering if the cold supply into the boiler is still restricted in some way, resulting in a lower than expected hot water flow. Here is a photo of the pipes, there are two devices and a tap attached to it, each of which looks old and worn. Is it worth me trying to replace them or can I just swap this whole length out for a straight piece of copper?
Should the tap be fully open or half way?
What does the 'dial' at the bottom do and should I be checking it?

Thanks again!
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Mon Jul 18, 2016 1:15 pm

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