Baxi Combi 105e correct operation query (CH)

4 Oct 2005
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United Kingdom
Hi there!

I've got a Baxi Combi 105e (not instant) and within the last couple of days it appears to have developed a fault with CH.
The HW heats up OK but the radiators are not getting hot and you can easily put your hand on them with no burns.

I checked the boiler and the pressure showed 3 bar! The manual states normal operating pressure is between 0.5 - 2.5 bar.

So, I call in British Gas (I'm on their Homestart or whatever thingy!). Engineer turns up today (I'm at work at this point & my wife's at home). He looks at boiler and after a couple of hours (needed a routine service anyway) says he's fixed the boiler, tested it and it's OK. He also said that the radiators have lot of sludge and it would be best to have a "powerflush" fitted to alleviate - £780 to you guv!

Fast forward to me getting home and radiators are still lukewarm! What gives?

So I look at boiler and pressure is still at 3 bar!! Quick call to BG and someone's coming back tomorrow!

Now to the crux of my post:
What is the correct operating procedure of the boiler for CH? When the CH "kicks in" the orange flame neon lights up. The red temperature neons light up to 80 degrees. After about a minute there's a click and the neon goes out. The red temp neons then go out till the 30 degree one stays on. This cycle repeats ad infinitum but the highest neon that stays on is 40 degrees. Is this normal? I must confess that before now I've never really looked at the panel, but I would presume that the flame would stay on and the neons would continue to rise and stay on to a higher temp?

Also, powerflush for sludge. Is this for real or just a way for BG to get more money?

Any thoughts would be appreciated! Sorry for the long post.
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Screeming POWERFLUSH is the last resort a simple inspection of the return filter on the boiler is the easiest place to start.........followed by many other checks before the wallet is opened...
Screeming POWERFLUSH is the last resort a simple inspection of the return filter on the boiler is the easiest place to start.........followed by many other checks before the wallet is opened...

Thanks Baxmax, thought it might be a way of trying to screw money out of us!

Could anyone please answer my question about operation, i.e. the boiler seems to cycle rather than constantly heat up the CH? Thanks
Because it has reach guess is as baxmax has said, blocked filter, pump gone or bad sludge.......or all 3! Maybe other things but if you start on those 3 i doubt you will be far off
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Thanks for the replies!

Update: Last night I bled the radiators! Lot of air! Pressure dropped to 1 bar.
After 1 hour pressure had returned to 3 bar :eek: and radiators only luke warm.

Any ideas? Still waiting for BG engineer
I think BG might just endup upsetting you. If its due to sludge/circulation you might find they wont cover the repair unless you have the system flushed by themselves or a third party flush then re-inspected.

The pressure problem could be due to the circulation problem...heat not disappeating away from the boiler so i dont think id worry about that until the central heating issue is repaired.
Id imagine a pump problem would affect the hot water too. Id definitly look at having the return connection removed and inspected. Its more than likely a simple blockage somewhere. maybe concider having an independant engineer look over the system.
A powerflush is excessive but if you think it would benefit the system it might not be such a bad idea and double check but any further powerflushings the system needs would be free if done by BG?

Ray84, thanks for the info.

BG engineer thinks its heat exchanger - pressure is high, cold water goes into boiler when shouldn't causing pressure to remain high and therefore not letting boiler get to high temperature.
As they've got to order part in it'll be replaced on monday. Thankfully weather has improved!!!!

I'm going to wait to see if this fixes the problem before worrying about powerflush.

BTW, is it possible to remove any sludge from system as a DIY job i.e. is it something we can do ourselves?

it will be the heat exchanger but this is cleanable it does not need to be replaced, i have a baxi 80e combi (piece of crap) i have cleaned the heat exchanger, it can be done under a good pressure tap with a lot of shaking or connected to a powerflusher as a heating engineer i connected mine to my powerflusher, i have done many by tap though, If you need to powerflush your system do not us BG they are a rip off,
I've got BG to pricematch a local quote for powerflush (much cheaper :LOL: ) but still don't really don't want to spend any more money than necessary so my question still stands, is it possible to perform a powerflush myself, or at least something like it?

it is possible to use the incoming main however without heat this will maybe at best solve the problem for a short while. you can remove each radiator in turn and flush through with a hose and main supply giving the a good shake and hitting them with a rubber mallet, as most the sludge will rest in the rads. again though warm/hot water is the best result
Thanks for all the helpful replies!

Well, BG returned and replaced the heat exchanger and the pump! Pressure returned to normal (1.5 bar) and so far (3 days) boiler is a-ok!

Only one minor (self-caused) problem: Before boiler was completely fixed I thought I'd be clever and bleed the radiators to see if that would fix high pressure problem. Except I did so with the system running :oops:
2 days after boiler was fixed pressure dropped to zero and no hot water :eek:
I repressurized boiler via feeding loop back to 1.5 bar and so far (fingers crossed) it's all working ok.
I presume I introduced air into the system?

Would any of you boiler/CH guru's agree I should now re-bleed system but of course with system off?
I ask as radiators are still not as hot as used to be before boiler broke. Or is this a sign I need the dreaded Powerflush

Just been reading around a bit more and found several topics about radiators that are hot at top and cold at bottom.
In this case bleeding is not needed but perhaps balancing the system would be more appropriate.

Any thoughts on this? Should I try to balance the system first?


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