No heating

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Maisie moo

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I will try give as much info as possible to help.
Vaillant ecotec 24. Problem started a few weeks ago with F75 error code and having to keep resetting the system to get hot water to work. I changed the pressure sensor and sorted out the F75 error and the pressure now rises as it should when the boiler turn on. Set at 1.5 and rises to 1.9 when the boiler is working. As it's getting colder outside I turned on the heating and it isn't getting the radiators hot. I can hear and feel the pump working so it isn't that. I thought it might be the diverter but as I turn the water on or off at the tap I can see the rod pushing in and back out accordingly and no water drops from this either. Hot water still getting hot at the taps by the way.
When I initially turn the heating on the boiler fires up as normal but then turns off as the temp rises to around 75/80 and the pump over runs as it should. Could it still be the diverter valve even though I can see the rod moving???
 
No it is a well known problem with that boiler, your system water is dirty and the boiler cant handle it, you can do repairs but you will have to sort out the system water
 
Thanks for the reply water that came out when I drained to fit new pressure sensor was running really clear.
 
If this is the first heating run since you drained & refilled you may have an airlock somewhere.....or have you closed some isolating valves & not reopened them?
 
I have bled the radiators apart from one could it be this one radiator? It's a bitch to get to.
 
Usually if you haven't bled a radiator the rest will still work. You may have an airbubble trapped in the main pipe run from boiler to rads (if, say, the flow & return go up from the boiler then drop down to the rads you can end up with air stuck at the top of the loop).
 
Have a look at the pipework, see if you can spot any high points (up, long straight run, down shouldn't be a problem, up, short flat, down might be).
Try bleeding with the pump running (tricky on a pressurised system, you'll need a friend on the filling loop) the rad nearest the suspect pipework. If you have modern radiators (where the bleed valve is in a hex plug with an o ring seal) it can be worth bleeding flow then return by removing the plug;
Close the lockshield valve, count how many turns it takes to close it.
Open fully the TRV or normal valve.
Bleed (or remove plug), let water flow for 10 secs or until you hear some major gurgling
Close bleed/replace plug. Top up system if pressurised
Close TRV or normal valve fully
Open lockshield fully
Repeat bleed.
Close bleed/replace plug
Set lockshield to wherever it was before you started.
Oh, here's a thought, have you got one of those Magnaclean filters/dosing pots? Have you checked to see if that's full? (Use isol valves unless you want a big mess)
 
Think I will get an engineer in lol. Thanks for all your help oldbutnotdead but all that sounds a bit much for my simple DIY brain.
 
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