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I have a overheating issue very few days with my boiler when the UFH is on have to reset CH and HW all working perfect. My UFH is polypipe with a Baxi boiler. I have had a baxi engineer out to look at the boiler who has advised that the UFH needs balancing as the heat from boiler is not dispersin. I have also been advised that maybe installing a pipe thermostat on the return flow pipe. I am a complete novice guys. Any help is appreciated. Quick pick of manifold attached.

A004516D-BBBE-4B1F-9A62-978450DBB673.jpeg
 

Chalked

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Gas Engineer
When your boiler fires. The heads on the manifold have not opened. The boiler has nowhere to pump , so overheats. An auto bypass will allow the flow of water to be continuous.
Modern manifold controls have a delay timer, to allow the heads to open before the boiler and pump kick in. The heads can take 5 minutes to open.
 
When your boiler fires. The heads on the manifold have not opened. The boiler has nowhere to pump , so overheats. An auto bypass will allow the flow of water to be continuous.
Modern manifold controls have a delay timer, to allow the heads to open before the boiler and pump kick in. The heads can take 5 minutes to open.
Can you please advise if this is something I can do myself? Sounds like I need a plumber out to sort it out is this correct? Thanks in advance
 

Chalked

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Does the underfloor work ok? As polypipe thermostatic mixing valves are renowned for sticking.
The system would need looking at to determine if a bypass would cure your problem.
Where are you based? There might be someone on here who could help.
 
Does the underfloor work ok? As polypipe thermostatic mixing valves are renowned for sticking.
The system would need looking at to determine if a bypass would cure your problem.
Where are you based? There might be someone on here who could help.
The underfloor works but I’ve never thought it had worked to its potential and now I’m getting the overheat issues. I am based in Preston. If you can get someone that would be marvellous. Thank you
 

ShaunCorbs

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I would say your boiler can't modulate down to a low kw eg just enough for the underfloor heating so it's just overheating

Does it work with let's say hot water on and your underfloor
 
I would say your boiler can't modulate down to a low kw eg just enough for the underfloor heating so it's just overheating

Does it work with let's say hot water on and your underfloor
Yes it works when hot water is on. The temps on boiler are fine when CH and hot water are on 60-70. When underfloor fires up temp goes up to 90
 

ShaunCorbs

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What's the kw size of the boiler ?
 

ShaunCorbs

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Do you know the heat load of your under floor eg every circuit ?
 

ShaunCorbs

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Should be on your underfloor plans if you have them
 

ShaunCorbs

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Spot on and there's your problem

Your boiler will only modulate down to around 7kw and your biggest loop is 1.9kw

So your way under the min the boiler can cope with

You have a couple of options but it's not going to be cheap and involves ripping up some floor boards
 
This
Spot on and there's your problem

Your boiler will only modulate down to around 7kw and your biggest loop is 1.9kw

So your way under the min the boiler can cope with

You have a couple of options but it's not going to be cheap and involves ripping up some floor boards
Whats my options please?
 

ShaunCorbs

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Your easiest option is to put a rad somewhere on the main returns that can increase the capacity upto 7kw

Some more options eg low loss header or change the boiler for one that has a lower modulation rating
 

ShaunCorbs

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This is excellent information. Will this definitely sort out the issue?
If you can get the lowest loop upto 7 kw yes

At the moment it can't get rid of the heat eg it's making 7kw and only requires 1.8 kw etc
 
If you can get the lowest loop upto 7 kw yes

At the moment it can't get rid of the heat eg it's making 7kw and only requires 1.8 kw etc
The problem is finding a competent plumber to explain this to. I have had so much conflicting information. What you have advised seems to be spot on! Is this why the boiler cycles on and off? Is this normal for underfloor heating? The rad option is probably going to be difficult as my boiler is in the kitchen and it is a tiled floor. Would you recommend a boiler replacement make and model?
 

ShaunCorbs

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That's normal esp with the influx of fast training etc

Yes can't get rid of the heat quick enough

And unless everything is calculated eg sized right and loadings so they meet the min

I don't think your going to get one with a low enough modulation eg down to one or two kw
 
That's normal esp with the influx of fast training etc

Yes can't get rid of the heat quick enough

And unless everything is calculated eg sized right and loadings so they meet the min

I don't think your going to get one with a low enough modulation eg down to one or two kw
So my only option is to fit a radiator?
 

ShaunCorbs

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Gas Engineer
Yes to bump it upto 7kw

Or to live with it, which isn't the best option
You seem like an expert. Auto bypass, pipe thermostat, mixer valve all these potential repair options that have been advised by different users/ plumbers will any of these not do the job? What’s the worst that can happen if I left it as it is? Baxi have changed the thermostat and the issue of boiler overheating and switching off has not been apparent lately. Will I need to change thermostat every couple of years on the boiler?
 

ShaunCorbs

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Auto bypass will help,

Pipe thermostat won't do bugger all
Same with a blending valve

And will put undue wear on the boiler but shouldn't harm it that much
 
Auto bypass will help,

Pipe thermostat won't do bugger all
Same with a blending valve

And will put undue wear on the boiler but shouldn't harm it that much
I shall look at the radiator option for now. Thankyou so much for all your informative advise. It’s truly really appreciated.
 

ShaunCorbs

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Plumber
Gas Engineer
More than welcome
 
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