Discuss Boiler cycling on and off. in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Tats

Hi all,

I recently had to condemn an old baxi boiler due to CO leaking into the kitchen. it was a system boiler on a C plan. Has 22 mm pipe to about a meter after the motorised valve and reduced down to 8mm microbore to feed the rads. The previous electrics were an absolute nightmare. The homeowner was an electrician by trade (retired now) And it seems that he passed time wiring everything he could into one timer which he was using as a junction box.

I got a Worcester green star 15 ri to replace the old one and bought the Honeywell s plan smart fit. The installation went fine with minimal snags. I drained down and cleaned out the pipes, installed two new motorised valves making it an s plan set up. The new electrics went in fine and now make sense!
The problem i have now is The boiler fires up for a few minutes then turns off, and back on again a few minutes later on both central heating and hot water. This repeats until the programmer is switched off. Also 3 out of 7 radiators are not working. One has never worked according to the homeowner however the other two did. I have bleed all the air out of everything I possibly can. One of the rads has heat in the pipe but it isn't going Into the actual radiator. The valve opens and closes fine. I've took it off and checked its insides and it works as if should so I can't understand why the rad isn't heating.
i have drained down the system multiple times, took the rads off the wall and cleaned them individually removing massive amounts off gunk from each one but still it's not playing ball! I realised that I misread the instructions and never installed an automatic bypass. A Y plan doesn't need one but S plan does. This will be fixed on my next visit! Could the lack of bypass be causing it to constantly cycle off and on?
The other thing I thought it could be is the flow and return are reversed. I checked to see what heats first from everything being cold. The return pipe by the cylinder seems to get a bit of heat before anything else but then my pipe leading to the pump etc gets boiling as it should so Im really not sure!

any ideas what else I could be looking at here? Blocked pipe work? Reversed flow and return? Any help is greatly appreciated!
 
Its sounds like one of my past nightmares!

8mm pipe! sounds like you have an air lock, is the system open vent or sealed?
 
It's breaking me!
It's open vent. I've done everything I can think of to get air out of There. Its hiding well and refusing to budge!
 
Ok, mine was an open vent with 8mm.

I was on it for about 1 1/2 days, i did crack it in the end.

I forced the air out using mains pressure cold water.

Worked a treat!
 
circulation problems from air locks or blockages at a guess, take off rads that dont work and open each valves and see what flow rate you have. yo can atttach a pump and try and push the air out, if you push a blockage it may move to another part of the system.

8mm is a pain in the rear, id consider taking the rads outside and flushing on a hose pipe, maybe even running a strong acid cleaner through if you can get circualtion around the system. protect the boiler of course.
 
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