Worcester Bosch Heatslave 15/19 Lukewarm Radiators

[sotontotton]

If anyone can give me pointers it would be much appreciated. I've done loads of googling but yet to find any clues apart from 3 way valve.

I have a 15 year old Worcester Bosch Heatslave boiler that has been working fine until recently. Hot water not an issue, but 8 times out of 10 when the heating clicks on the radiators only get luke warm. When I feel the pipes in the boiler the one at the back marked 'rear of appliance' gets very hot while the 'central heating flow' is luke warm. Today I removed the 3 way valve head and change the synchro motor, checked free play in valve shaft and also made sure the gears weren't jumping. This has made no diffrence and also upping the heating knob changes nothing. I'm thinking there is something wrong with the 3 way valve inside but obviously that will need a drain down and some work to get out. The water pump was changed 2 years ago by Worcester bosch.

Any ideas before I give the technical WB line a call?

 

[oilhead]

If the heating flow pipe is not getting hot, then there is a problem with the diverter valve in the boiler, assuming your 'new' pump is OK, and isset on the high speed. What diverter valve is fitted in the boiler? (Honeywell Number)

 

[sotontotton]

Thanks for the reply.

The diverter is a 3 way Honeywell model v4044f1125. I have the pump speed up at 3. I did a test so turned down boiler temp so when it triggered it started up and I could hear the 3 way valve operate. It did operate very slowly from the default water to the heating. I did move the spindle easily using my fingers with the head off so no restriction there.

 

[oilhead]

Any restriction in the heating circuit would normally let the flow pipe still get hot, so the problem must be with the diverter valve. There is a rubber ball on the lever which may have disintegrated and blocked the flow port, but it may be best to consult a professional for a check and thir opinion.

 

[sotontotton]

Thanks for the info oilman. I've ordered a new complete 3 way valve so will update once installed with the results and a pic of the internals of the old one should there be something obvious.

 

[sotontotton]

New diverter arrived today so went to work on the boiler. Couldnt get complete valve out of boiler so replaced the head and the top plate that contains the rubber ball. Not sure the one i took out was origional or not as was a square plate rather than the new curvy one. Rubber ball looked slightly swollen and wear on bottom part. The shaft on the new one moved more easily than the old one. Put it all back together and tests so far have hot radiators rather than lukewarm.

Cheers oilman for your help.

 

[oilhead]

Thanks for feedback, glad you're sorted

 

[sotontotton]

Spoke too soon.

We seem to be back to random hot radiators, hot radiators at first then go warm before room stat switches off boiler or radiators just getting warm. Looking at the pipe at the rear of the heatslave boiler labelled 'rear of appliance' this gets very hot when the heating is on and radiators are only warm. When radiators are hot this pipe is only warm. So I changed the head and rubber ball/spindle on the 3 way valve and it's made no change. Could it be that somehow the PCB supplies voltage to the 3way valve and that voltage is dropping causing the valve to open slightly and bypass water? I'm calling worcester bosch technical tomorrow to see if they have any ideas. The only other thing is the valve body isn't the new one but checking insides of it although discoloured no deposits or blockages.

 

[oilhead]

You need to check the outputs from your thermostats. If the DHW stat is demanding, then heating will cut off.

 

[sotontotton]

Its doing it when the hot water isnt in demand and when the heat store isnt being heated. Hopefully i will get something out of the phone call to WB technical line.

 

[oilhead]

Have you checked the outputs on the PCB with a meter? The burner will not necessarily always fire.

 

[sotontotton]

Not checked the PCB outputs but have an update. Called WB technical and explained the full problem to the guy on the other end and after a confirmation of the boiler he said it's a diverter issue. As I've already changed the head and internal ball valve/spindle I decided to replace the valve body as well so a complete valve. Problem the same after that. I then felt the pipes either side of the pump and they were cold with the boiler firing and pump supposedly running. I took the pump out and connecting to mains that rotated fine and a fingered stopped it with some force. Unsure I got a replacement pump and again same problem. The 3 way valve moves, the boiler fires then the pump starts with a small flick down on the pressure gauge. The pipe marked 'rear of boiler' gets red hot but pipes either side of pump are luke warm. If I switch to heating water that's fine and I can feel the heat both sides of the pump. I've even opened up all the valves including trv's think there is some restriction somewhere. The only thing I notice now is the heating works fine after the hot water has been on. If I switch the hot water off at the boiler I can't get the heating above luke warm. The burner is firing all the time demand is on for heating.

I can feel my 3rd WB guarantee fix it in 3 years coming on. My only worry is some random blockage in the central heating pipework that wouldn't be covered.

 

[oilhead]

Did you bleed the pump and heatstore circuit properly? Sounds like you have an airlock.

 

[sotontotton]

Thanks for sticking with me on this oilman.

I unscrewed the cap on the heat store so the autovent expelled air and I also undid slightly the silver cap on the pump again to let air out. Couple of things I want to look at today. I was going to get a meter on the pump cable to see voltage coming from the pcb. I might connect the old pump to the pcb (dry test), turn down the thermostat on the boiler then turn the room stat up to get the boiler going. Be interesting to see the pump behaviour. One observation I had last night was how slow the 3 way valve moves when engaging the heating. I'm sure I read somewhere the 3 way valve should move as quick as the springs move it to its default position.

If the tests look ok then it must be an airlock.

 

[oilhead]

Good luck! The 3 way valve will close quickly on the springs, but will take about 30 secs to open with the motor. Also, you may get a clunk sometimes if the valve moves with the pump running. Don't worry about that, its the pump flow helping the valve move.