Which Heat Exchanger Should I clean???

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Hi.
I am having problems with my Main Combi 24HE boiler. DHW works fine (although pressure isn't great) but my CH keeps turning off. The boiler stays lit for approx 45 secs then turns off for 3 mins (This cycle just carries on).
I've read the boiler manual and it explains that the boiler will turn off for 3 mins if...
"3. When the flow temperature exceeds the setting
temperature, a 3 minute delay occurs before the burner
relights automatically (anti-cycling). The pump continues
to run during this period."
I think the heat exchanger may be blocked with limescale and other deposits.
I had carried out a DIY flush (prior to this problem) using mains pressure and sentinal 800 but I think this may have added to the problem. I think I may have moved alot of sludge and deposits from the rads into the boiler.
My question is...Which heat exchanger should I remove and clean? Primary or Secondary?
Any help/tips would be greatly appreciated.[/i]
 
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Usually if your secondary plate h/e is blocked/scaled it has an effect on your hot water output (i.e. Not getting hot enough). You say pressure's not great, is your cold mains pressure adequate ? You could take the plate out and try descaling it. But, i would price a new one as i think they're about £40ish and when you price cleaner/time/IF it works sometimes not worth the hassle.
 
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Thanks for your replies!
The cold water mains pressure is fine. Its just when I run a bath or shower I have to turn the tap down for the heat to be maintained. If I open the tap up too much the temp drops (Bath with thermostatic tap/mixer upstairs directly above boiler).

But...I can run a hot bath or kitchen tap for as long as I like and the boiler won't cut out. It only happens when I select CH.

So I thought the the heat plate exchanger was probably OK (This is what heats the DHW...'I think') and therefore it was the primary or secondary (or both) heat exchangers that were blocked??? I'm getting all this info from the installation guide (link below)

http://www.mainheating.co.uk/docs/Main_Combi_24_HE_Installation_and_Servicing_Guide_2011.pdf[url][/url] PAGE 8

I might price up the cost of a heat exchanger rather than cleaning it. But any ideas as to which one I should try first?

Also...I should add...I have already replaced the Safety Thermostat and the Central Heating Temperature Sensor - They were fairly inexpensive and easy to replace...But it didn't make a difference! D'oh!
 
:eek: did u take out the filter?...!
Thanks MC2012. I haven't yet. I was just having a look in the installation guide and there is an instruction on Page 36 on how to remove and clean the DHW filter. I will have a look at this tomorrow but would this affect the CH?
 
Look at page 10, it shows the layout of pipe work connections, look at the right hand 22 mm connection, it should have a nut on the end similar to the one you were referring too on page 36. There's a metal filter in that one too, if its blocked it will cause the same issues your are experiencing.
 
Cheers MC2012!!! I'll be checking that filter 1st thing tomorrow morning. I'll let you know how I get on!
 
MC2012 - Your a legend!!!!

I removed the blanking nut from the heating return as you said...But there wasn't a filter or gauze. I then removed the heating flow blanking nut and found an extremely clogged up filter/gauze! I removed it and cleaned it up. I then refitted it on the heating return.
So I'm guessing whoever fitted the boiler put the filter on the wrong 22mm pipe.
Anyway...Now the boiler is working perfectly well! All the rads are heating up and I'm now walking around in a pair of shorts!!!

You've saved me alot of time and money!!! A massive thanks to you all for your help!!!

:D
 
Might be worth investing in a Magnaclean to protect the boiler from dirt in the system...
 
Yeah it should have been on the return but its an easy mistake to make on installation.
Not a problem glad its sorted for you and saved you paying out for more bits you didn't need. :D
 
Might be worth investing in a Magnaclean to protect the boiler from dirt in the system...
Cheers Muggles! I've been considering a filter. Magnaclean or a fernox. But the CH return is in a really awkward place. Its right behind the CH flow and really close to the wall...Prob too close to get a pipe cutter in. I might have to get it professionally fitted as some pipe rerouting may be necessary...
 
I bought a Spirotech MB3 to protect my new boiler, I like the all brass construction.

It's caught some magnetite already even though the system would be considered clean, and was flushed before the new boiler was installed. Only a bit mind, but I think there's only a bit in there. I didn't fancy it settling in the bottom of a brand new low water content heat exchanger.
 

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