Grant Oil Combi DHW ok - But no CH... Help appreciated.

[nr0]

Go easy on me please, im new to this !!
I have a Grant Oil Combi 90 V3 MAX.
Its around 4yrs oil, and other than needing to replace the diaphragm once or twice, its been trouble free.
Up until a slightly cold snap this week, when i noticed the CH wasnt working.

Ive removed the flow switch from the diverter valve, and this seems to be operating as it should (spindle pushed out when hot water tap is turned on).
This activates the flow switch which fires up the boiler for DHW.
Ive also removed and replaced with a loop the room stat cables, to eliminate that.
I also today, flushed out the system incase it was down to a blockage or poor flow (what came out was surprisingly clean, some discolour, but not sludgey).

The only other thing ive noticed - that doesnt seem right, but im not sure.
The pump seems to be running most of time, and is running hot.
Im not sure if this is related - but somewhere along the line, the boiler isnt been told to fire up when there is a demand for CH.

Any suggestions appreciated.
(My old boiler had a motorsied diverter valve, this boiler doesnt seem to - just the housing for the diaphragm which also has the flow switch mounted on it).

Thank You

 

[kimbo]

The switch on the end of the diverter is a dual microswitch and not a flow switch, First of all you need to make sure the real flow switch on the incoming mains inside the boiler is not stuck in the on position, this can be quite common. Disconnect the flow switch terminals inside the control panel, it should be marked and easy to find. If the flow switch is a problem by disconnecting it you will allow the boiler to go to CH mode.

 

[WHPES]

Assuming its one of the original Combis (not the current Vortex ones) you will probably be referring to the brass diverter valve thingy. Chances are the gubbins have jammed and unfortunately you can't repair it. I replaced one recently - Heating World of Spares have it for sale on their site and are the cheapest price.

 

[kimbo]

sorry this version has not got a flow switch.Check the pump has not airlocked undue the large nut on the front and make sure there is no air in it, these had a habit of airlocking as it is a downward pump.

 

[WHPES]

Make sure all the pipework is free from airlocks. Kind of assumed this would have been checked anyway.

Is this the thing
GRANT BRASS DIVERTER VALVE | MPCBS20

 

[kimbo]

I dont think it would be the diverter WHPES because the pin is coming out on demand forhot water therefore the diaphragm is working. If the diaphragm wasnt pushing the pin out there would not be any hot water but there would be heating.
You need to check that there is a demand for heating ie a live from the programmer to the boiler also I do believe that on this boiler they use a pcb for the the control stat, these fail quite often but you need to check you have a live supply in to it, I,m afraid if electrics is not youre thing you may be struggling.You need to check things through methodically so you can dismiss certain things.

 

[WHPES]

Check for airlocks

Call Grant tech support. They are usually pretty helpful

 

[nr0]

Just to update guys.
I removed the pcb to find a small blackened area, and thought something had burnt out. So I replaced - with no luck, still not heating.
I then replaced the diverter valve - when I removed the old one, the rear (inlet or outlet - not sure which), was black and clogged up.
With a CH flush out and new diverter valve she's brand new.
Thanks for your suggestions.
NR