Problem with heating/hot water

[Mark Turvey]

Ok so firstly I have a glowworm 18hxi boiler with Honeywell programmer, hot water set for half an hour twice a day and heating on continuous and using thermostat to control temperature. All was working perfectly until this weekend when I noticed it was colder than usual in the house so I checked the boiler to which I had fault code f26. I reset the boiler and it seemed fine for a while but only upstairs radiators got hot so i assumed the pump was on it's way out. I have replaced the grundfos pump with new and still the same problem. It is inconsistent though as the heating came on for hours at a time without me touching it over the last few days and a bit of balancing and the downstairs rads do now get warm but not hot. Also the hot water will not come on at all, I've tried turning the thermostat for c/h down and then putting h/w on extra hour setting and it does nothing. The two way electric valve leading to the pump won't even open for h/w. The boiler itself is acting rather strangely also, it fires up reaches about 70 or 80 degrees then turns off and let's the temp down to about 20 before kicking back in whereas it used to stay lit and mainain temperature between 50 and 80 ish. I can get hot water by activating c/h then manually opening the motorised valve going to the h/w tank. It's really messing with my head now I've bled the system properly a couple of times, the only problem I've got which has been that way since I moved in three years ago is the main bathroom radiator only ever gets Luke warm and doesn't flow like it should, I've never bothered about it so haven't fixed it. Also whilst bleeding all the rads I noticed that the one in the spare room doesn't displace any water or air from the bleed valve but the red gets hot all over. The house is only 10 years old btw. Any help would be much appreciated I'm scratcing my head on what to do next. Thanks in advance.

 

[Mark Turvey]

Sorted the red in the spare room, put a pin in the hole where the bleed screw goes and let's just say I got a light spraying to the face. Still no hot water and heating has been on and off all day with little effect on the temperature of the house. It just isnt circulating enough hot water. Any help massively appreciated.

 

[Frog67]

Sticking zone / 3 port valve restricting flow and causing thermistor to knock off boiler (perhaps)

 

[Mark Turvey]

Thanks for replying, I have a two port valve coming from the boiler which was replaced early this year, seems to be operating fine as soon as I activate c/h the valve opens and hot water comes up the pipe through the valve to the pump....