Erratic water temp and boiler crashing under load

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18 Feb 2014
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Yorkshire
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Hi, iv got a vaillant ecotec 28 boiler.
Problem I'm having is that it only seems to work when most of the rads are closed off.
Also the hot water temp is erratic.
The pressure sensor has been recently changed, the expansion tank has been checked and the filter in the hydro block checked by a gas certified friend.

It's showing up a f75 code when it crashs. I know this is a very common code on this boiler.

My mate is too busy to do any more on it and I just want to know what it could be before I start calling round engineers

Ta
 
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Is the pump spinning ? Take centre screw out and poke a terminal screwdriver in (protect under pump as a little water will come out) also is your heating system water clean ? Not saying this is the answer but its a start.
 
Thanks for the help
I assume the pump if functioning as I can feel it vibrating sligty when in use.

Is it worth me draining the system to check the pump?

There wasn't much silt in the system when the sensor and filter were checked/changed.

It can run fine for 24 hr straight and then as soon as I open up another rad it crashs. Driving me crazy!
 
It wouldnt do any harm to drain the boiler and remove the pump head, its only 4 allen bolts and easy to take out and refit, try and catch the water in a basin as you drain it and see how dirty it is, also how dirty the pump impeller is will give you an indication on the water quality, it is quite common for the pump impellor to be blocked up or even sheared off but the motor just turns as normal
 
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Isn't this model one where the front cover is the outer combustion chamber cover and therefore should not be opened by a DIYer because it creates the room sealing?

If its a pink sensor then they are best replaced by the later black one. The gas reg person should have seen and acted on that though.
 
Hey
Thanks for the help with this.
Turned out to be crud in the pump, cleaned out the pump and back to normal now.

Thanks, matt
 
Glad we were able to help out Matt, afraid your problem will happen again if you dont get some cleansing and inhibitor into your system water though
 

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