Potterton Combi boiler driving me potty

[dja]

Hello, Our boiler is a Potterton Statesman Flowsure + Combi boiler.
A few days ago woke up to cold radiators Checked boiler and boiler temperature gauge was showing boiler at 90deg (it usually runs at 65-70). When I moved the diverter valve arm to manual position, radiators got hot but boiler was still controlling at 90 deg. When valve arm was moved back to auto rads went cold eventually and boiler was still at 90 deg. Burner would cycle much more frequently than normal to keep everything at 90deg. Boiler temp control knob didn't have any control of the boiler in this condition so I replaced the boiler thermostat but this hasn't changed anything. I'm wondering if some other thermostat has failed to cause the boiler to drive to 90 deg.(Heatstore stat or tank limit stat?). I replaced the diverter valve actuator about 3 years ago, so I would be surprised if that had gone again. Something has changed to make the boiler run hotter. Can anyone offer any help please.

 

[Agile]

It sounds as if the diverter valve MAY not be moving correctly.

But the main fault is likely to be the pump jammed.

See FAQ for checking and spinning the pump. Probably needs replacement or system desludging.

Tony Glazier

 

[dja]

It sounds as if the diverter valve MAY not be moving correctly.

But the main fault is likely to be the pump jammed.

See FAQ for checking and spinning the pump. Probably needs replacement or system desludging.

Tony Glazier

Thanks Tony, but if the rads heat up when the diverter valve is moved manually then this would suggest the pump is OK wouldn't it?

 

[dja]

Hi just to update. I've now changed the boiler stat, tank limit stat and the heatstore stat, with no change to the boiler behaviour, any more thoughts please.

 

[petit_pablo]

any more thoughts please.

Agile has pointed you in the right direction, you chose to fit more unnessesary parts.

 

[dja]

Yes but his direction can't be correct as the pump is pumping fine when I move the actuator lever to the manual latch position.(the rads then heat up...if the rads can heat up then pump must be OK) I've also removed the old valve actuator and the drive spindle to the mechanical part of the valve turns really easily and I can direct the water to any of the 3 positions (DHW, CH or Mixed)

 

[petit_pablo]

Then if the valve moves manually and doesnt move of its own accord then id be starting there.

 

[dja]

That's my feeling now. I'm ordering a new actuator today. I'll keep you posted on progress.

 

[Agile]

When repairing boilers its a matter of diagnosing and testing, not replacing various parts and ignoring others "because you dont think its faulty.

The diverter valve needs to be tested to see if 240v is being applied. If so then measure the motor winding and look for about 2-3 k.

The pump needs to be tested. See the site FAQ for how to do that.

Tony

 

[dja]

Thanks Tony. I have been trying to use the evidence available to try and sort the problem The reason for changing the stats is that the boiler was running hotter than normal so I believed that something had failed such that the boiler was being driven to a higher temperature and the stats were reletively easy to replace and cheap(ish) anyway.
As the rads get to normal temperature I suspect the pump is OK but I will search FAQs.
I also suspect that the actuator is getting 240 volts as when I fire the boiler up from cold and demand CH the actuator moves once electrically when the boiler gets to 85-90deg, but then sits in the DHW position forever. So I'll change the actuator but I'm also wondering if the main relay could be at fault. I know it sounds like I'm fishing in the dark but I am trying to do things logically and also changing any suspect part based on evidence , ease of change and cost.

 

[Agile]

If the valve is moving then the motor is OK. The microswitches might be failed but thats not so common.

More likely to be something else.

Tony

 

[dja]

OK, but it only moves once when the boiler first gets to it's (too high) temperature, even though the boiler may be on for hours and demand is CH and occasional DHW. I would expect it to shuttle around quite often.

 

[dja]

Hi Chaps, Been away for weekend and this morning decided to do a test from stone cold to give you more comprehensive clues in the hope of bottoming this
So this morning switched boiler on. Settings were CH constant demand, Boiler at 15deg and 0.8bar. Diverter valve was set at DHW position (observing this with diverter actuator removed from mechanical valve but still electrically connected and watching actuator for movement) and diverter valve spindle set at DHW to match. Pump started running immediatly power was switched on (should this be?). Burner ran until temperature gauge got to 88deg, pressure 1.6bar, pump still running and no control from (newly replaced) boiler control thermostat.Temp peaked at 92deg.
After 50mins (pump running all time and no movement yet from diverter actuator) burner fired up again at 86deg. Burner off again after 2 mins at 90deg/1.6bar.
I then drew some hot water from the kitchen tap, plenty of hot water but burner didn't fire up as expected. I then moved the diverter mechnical valve spindle to CH and rads then got hot. As rads got hot temp dropped to 65deg (cool water coming through return pipes I guess) and then rose steadily with burner on until burner switched off at 92deg but 2,4bar (can't understand why pressure should be higher in CH mode). Throughout all of this time diverter actuator has sat in DHW position, pump was running throughout and boiler control thermostat seemed redundant. Switched boiler off at this point to scratch head and write this. Appreciate the feedback chaps but anymore clues.?