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PostPosted: Fri Sep 22, 2017 12:24 am 
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Hello Everyone,

I have a Baxi 28HE system boiler. Like many I haven't used it over the summer period and when I fired it up it was making loud knocking and banging noises.
The upstairs radiators were getting hot and then they just stayed warm but nothing for the downstairs ones. The hot water works ok but the heating is poor, the boiler only reaches around 35-40 degrees although the water is heated up fine.
I have drained the system to see if it was an air blockage or sludge and the water was on as last year I drained it down and added an inhibitor as well.
Filled the system back up, bled the radiators etc and added a sludge cleaner. Fired it up again but it's the same and I don't believe the cleaner is getting around the system properly as there is no flow or very little flow reaching all the rads.
I have checked the pump and it's not seized, i unscrewed the pump screw at the front and I could move the inside using a screwdriver although it still may be faulty I'm not sure.

If anyone can share some light on this it would be appreciated. Trying to get it sorted whilst we still have fairly mild weather as I have a couple of young ones as well.

Cheers Dean


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PostPosted: Fri Sep 22, 2017 7:19 am 
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Hard to say without being in front of it, but could still be pump not circulating properly, or the heating zone valve faulty.

Do you have an auto bypass on the system?

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PostPosted: Fri Sep 22, 2017 7:44 am 
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Hello Dave,
Thanks for reply. I've checked the online manual and it says yes there is an automatic bypass on this model.
Baxi megaflo system 28HE GCN 41 075 48

Cheers


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PostPosted: Fri Sep 22, 2017 7:47 am 
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I tried to put some photos up as I have the front of the boiler off but it keeps telling me they have too many pixels to post them.

http://www.baxi.co.uk/documents/7219674 ... nstall.pdf


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PostPosted: Fri Sep 22, 2017 5:43 pm 
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As that is a built in by-pass, all it does is protect the boiler rather than act as a proper system bypass.

Banging and knocking noises are sign of very poor circulation usually.

Pump can spin, but not actually circulate sometimes.

As said, also check your heating zone valve is working.

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PostPosted: Fri Sep 22, 2017 7:39 pm 
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Ok thanks. Will check when I get back in approx 30 mins. The zone valve I believe is in the airing cupboard. It's got a metal casing around it and a switch that can go from side to side?


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PostPosted: Fri Sep 22, 2017 9:36 pm 
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So one side is for heating and the other for dhw, is it just a case of checking if both sides are hot?
It has a switch that says auto on one side and Man (I take it manual).


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PostPosted: Sat Sep 23, 2017 8:53 am 
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So I assume it is a 3 port valve then?

What happens if you lock it into the man setting?

Do the radiators get hot and the boiler run ok?

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PostPosted: Sat Sep 23, 2017 10:29 am 
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Locked it on 'man' and run the heating but it's still the same. Boiler gets up around 48 degrees and only 2/3 rads get slightly warm upstairs. The rest are cold.

Do you think it seems more a pump problem?

Perhaps the pump head needs changing?

The hot water is ok though. Does the hot water require the pump to be working or is that a separate thing? I would assume the pump is just for the heating as the water heats up ok and can run a bath etc.

Thanks


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PostPosted: Sat Sep 23, 2017 10:34 am 
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The valve is Honeywell V4073A 1039


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PostPosted: Sat Sep 23, 2017 4:35 pm 
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Pump is doing heating and hot water, so for now we have to assume the pump is ok, although HW circuit will have a lot less resistance than the heating circuit.

Looks like one of those new awful ERP modulating pumps from the diagram in the manual you posted.

What I can't get my head round, is that if it was a pump/circulation/blockage problem, I would have expected the boiler to heat up to around 70c at least, assuming this is the temp it is set to, possibly banging or getting noisy, before cutting out.

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PostPosted: Sat Sep 23, 2017 5:59 pm 
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.

What I can't get my head round, is that if it was a pump/circulation/blockage problem, I would have expected the boiler to heat up to around 70c at least, assuming this is the temp it is set to, possibly banging or getting noisy, before cutting out.[/quote]


Ah yes that is actually what it is doing.

The boiler goes up to over 75 degrees when I turn up the dial but only stays there a matter of 4/5 minutes then it knocks and bangs a lot and then the temperature gradually reduces to around 30 degrees, the fan and burner comes on intermittently but when thenboiler goes up to around 75 degrees again it will drop down.

We do get hot water but the rads are not good at all.

I've just turned the heating on again to check and when it reaches the higher degrees it's knocking very loudly, like there is air in there or something.

Does that seem like a pump problem? It's staying on the higher degrees at the moment but is very very LOUD.


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PostPosted: Sat Sep 23, 2017 8:26 pm 
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So hard to say from here, but it’s certainly a circulation problem, whether it’s the pump or something else can only be proved/solved by someone in front of the boiler and system.

Although the hot water appears to work, does the boiler still do the same when on for hot water?

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PostPosted: Sat Sep 23, 2017 9:14 pm 
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Thinking about it again, I am wondering if there is a filter in the return isolation valve set that could be blocked.

I can’t remember for sure at this moment in time

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PostPosted: Sun Sep 24, 2017 12:41 am 
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https://www.dhsspares.co.uk/product/bax ... gIqufD_BwE

That's the one on my boiler. Looks like there is a filter. I will turn off the flow and return on the boiler in the morning and check to see if it's blocked.

Cheers


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