Combi Heating Problem. How Water Fine!

John Stanwell

John Stanwell

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13 Mar 2018
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Hi all. I have a Baxi Combi 80 Eco and the hot water is fine, but last week when heating comes on the boiler fires and flame comes on, then after approx. 5 seconds goes down and then right out. This cycle of ignition - high gas flame (blue)- and then small flame - flame out continues, so not heating radiators, only 1 right next to it gets anything. Any ideas what to check? I have bled the radiators and the gauge reads 2 bar. Thank you for any help offered.
 
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Thanks for reply. A new pump was put in about 2 months ago and worked fine and quiet. How water is fine and pump runs ok for that.
1 radiator was cold and suddenly got warm 2 weeks ago, we have lots of 15mm pipe drops to downstairs rads.
Is there a filter to check? I couldn't see it in manual only a hot water one.
 
Ah see young Jedi!

More information.......
Lots of 15mm pipe equals bad install. New boiler new pipes work will good till bill,paid.

Years many later will show bad problems.

Physics show that hot water needs to flow fast enough way from boiler to stop it overheating. An old system sludged up will still overheat a boiler even with a new pump.

No idea if your boiler has a filter on the return or in the pump. Was a guess.

I've too much doodoo in my head to remember every boiler I work on......(y)

May I take this opportunity to Thank You for being polite and saying please and Thank You in your first post.

Many first posters omit these simple words.

I ignore these other people.........
 
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Thanks for reply! Just noticed the return connection to the boiler has PETENTED written on the valve and a screw cap. Loosened slightly and it comes undone. Perhaps if I drain tomorrow there could be a blocked filter in there with crap caught in it? Worth a go?
 
The pump is Grundfos just for your info. PATENTED is on the chrome boiler return valve cap. It also has a magnaclean below boiler and says on sticker in cupboard fitted by British Gas if that helps. I bled the magnaclean and water comes out in a good flow, all clean.
 
Sorry John, clean water means nothing. Clean the magna clean. If it's not been done for a while dirt will be inside the boiler.

99 percent sure your system is dirty.
 
Thanks again for replies. Going to drain down and check magnaclean and filter. Regarding thermistor I have heard that mentioned. I tested the resistance ant it was about 4k ohms, so not sure how to find out if faulty or not? Any advice regarding correct readings?
 
Magnaclean was thick with sludge and all cleaned now but problem exists. Plumber across road looked and reckons it's the PCB as it goes off/on off/on off/on as soon as gas dies down. Can I fit a new PCB myself or is it illegal? Thanks again for your kind replies all. PS> Small drip on bottom of magnaclean now after refilling. I didn't see a gasket though. Is this common? Can I fix the leak by winding PTFE around threads?
 
Could well be the pcb but would expect a lot higher reading on the thermistor around 12k (assuming it was taken with the water cool ?). The magnaclean sometimes have a black o ring undo and retighten bieng careful not to overtighten before you go down putting ptfe around.
 
Last edited:
Thanks Rochdalegas for help, much appreciated. Leak has stopped now. Checked thermistor when boiler cold, just over 12k ohms (as you stated it should be). I'm going to have to order a PCB up I think. are there any signs on PCB to confirm it's gone, or can it be repaired?
 
Can sometimes be better getting a fixed price repair from baxi once you take into account the price of a new pcb. Always worth having a look for scorch marks and checking harness connections
 
Removed PCB and refitted but problem just same as before. Can't see scorch marks though on the board. Could get one from ebay cheaper and see I suppose....
 
D

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