Worcester Bosch Heatslave 15/19 Lukewarm Radiators

[sotontotton]

Dry pump test went OK and no problems with the running of that. Random behaviour persists though with heating circulation to the radiators. I manually held the 3 way valve so the hot water circuit was closed but still the pipes either side of the pump were cold with the pipe at the back of the boiler marked 'rear of appliance' getting very hot. Airlock or blockage spring to mind but with it being intermittent I don't know.

WB technical wouldn't let me know the tests to perform on the boiler for obvious reasons. I normally get WB in to fix it for a fixed £280 Inc any parts, but don't want them rocking up to find out its an airlock.

 

[sotontotton]

Thought i'd connect up my meter to the pump today so these were the voltages and noted behaviour.

Heating luke warm no flow = 240/241v
Hot water only = 243/244v
Heating working fine = 242/243v

 

[Burnerman]

I guess you have bled the other two points on the top of the boiler?
John

 

[sotontotton]

I've bled the pump, manually the heat tank auto vent (to confirm it still works). The ones on top of the boiler are the three in the piccy.

Cheers

 

[Burnerman]

Did you get any air out of those three, and did you top the pressure up to 1 bar afterwards?
John

 

[sotontotton]

Thanks for the responses John.

I only got air out of the middle right side one so the combustion chamber one. I had the pressure at just above 1 bar and did try it at 2 to see if any air shifted. I've gone round the 9 radiators to check for air and nothing.

 

[Burnerman]

Hells bells
I don't get the fact that the pipes either side of the pump can be cool....with the burner on, the produced hot water is pumped either to the heatslave tank or around the radiator circuit.
Are you sure the bloody thing is actually spinning - centre screw off, small screwdriver poked through onto the impeller?
John

 

[sotontotton]

I won't tell you how much googling I've done on this ☺

I've unscrewed the cap and can see the pump spinning, have put a screw driver in to confirm and this morning held a screwdriver on the pump case and other end to my ear to hear rotation.

The water heating is fine, but the random no flow of CH is weird. I would say when there is heat in the store and boiler the flow generally returns. I did think of wiring the pump to the mains and switching it on when I test CH. If I get WB out I think they will change the diverter, pump again and probably the pcb. That was changed on their first visit 2 years ago shortly after we moved in.

I checked the Magnaclean I have on the return pipe for blockages, but that's clear.

Its tempting to leave it but I know it's going to bite me on the rear when the weather turns.

 

[Burnerman]

On a cold start on my own system (12/14 heatslave, 1999) the burner runs for around 10 minutes, pump running until the heatslave tank is satisfied. Then, if the heating thermostat in the dining room calls for heat the burner is continuously turning itself on and off - the off period only being a minute or so. Its 9 rad system. Is this about the same for yours, when its behaving?
Can you hear the boiler knob stat clicking when you turn it?
John

 

[sotontotton]

We have similar vintage oil burners

Heat store heating lasts about 8 minutes and moving HW stat up and down switches boiler on and off during that time. The startup procedure for the CH from room stat triggering is fan, burner then pump so guess 3 way is triggered same time as fan then micro switch fires the pump. I know this as the pressure gauge needle moves slightly backwards when pump starts. The CH boiler thermostat only switches the burner off if it's at level 1 so we have it at level 3 so I have never seen it off with just pump running.

 

[Burnerman]

If the rads are just lukewarm, is the burner off for long periods?
When mine is heating the rads, its only off for a minute before coming on again.
All seems to be ok with yours, to be honest - unless there is a blockage somewhere. When you opened up the diverter valve was part of the rubber ball missing?
John

 

[sotontotton]

If the CH thermostat is set to 1 then the burner is off for a minute or so but we have it at 3 so the burner is normally staying on. When I opened the 3 way it was mucky inside but not sludgy and the ball was intact and still attached. The system is clean but maybe there is something lose in the pipework somewhere.

 

[Burnerman]

For sure, I cant see anything suddenly causing a problem with the pipework....but I suppose its possible.
The heating out pipe is very hot, how about the return temperature? If the burner is on, the heat must be going somewhere. Is the domestic hot water hotter than before, do you think?
John

 

[sotontotton]

So when the heating is working and the CH pipe out is hot the return is hot. When the CH is lukewarm the return pipe is only warm and basically the pipe at the back of the boiler marked 'rear of appliance' with an arrow pointing to the back of the boiler gets very hot. I think the heat/water comes up this pipe then through the heat exchanger and can be felt where the pipe joins the diverter valve. All this with both side of the pump cold or luke warm at the same time. You can touch the heat exchanger and feel the heat although not excessive.

I really don't know how long this has been going on as it's not obvious. The hot water I wouldn't say is any more hotter than normal but we could have had this for 3 years. We use a woodburner when things get cold so it would be easy not to catch what's been going on.

 

[Burnerman]

What happens when you turn the heating stat on the boiler up to 5?
John