Bosch Heatslave 12/14 oil fired fault

[John.Stitch]

When I switch on the hot water only, the boiler takes 30 minutes to heat the water (3/4 of maximum temp) before it turns off, the radiators get hot as well as distinct from warm.

It used to take 15 minutes to heat the water and the rads only got warm not hot.

I have changed the combi care water softener every nine months, and drilled out the scale from the holes.

The boiler heats the rads fine no problems and the boiler works fine in other respects. It was serviced in January, the man appears to be a good bloke and knows his subject.

Any diagnostics suggestions please.

 

[oilman]

If you have spoken to him about it, he obviously doesn't know. It's either the diverter valve or flow switch. The combimate is not relevant to this problem.

 

[John.Stitch]

No I have not spoken to him since he serviced it on Jan 5th.

I had a closer look on the net. Two threads suggest that the diverter valve gets filled with crud and becomes the problem.

I took a closer look at mine, switching it on etc as follows:
Honeywell VC4613 actuator on top of the diverter valve.

Switching heating only on: small white plastic lever on side of diverter valve goes down and stays down.
Switching heating only off, plastic goes back up, and boiler stops.

Hot water only on: white plastic stays put. And switching off hot water, boiler stops

Heating on then hot water on, white plastic goes down then goes back up.
Then: switch off hot water and heating: boiler stays on.
If the white plastic is lifted the boiler stops.

So the white plastic is the valve operating correctly.
Or is it only the actuator?

Do I have an electrical problem or a valve problem?

 

[oilman]

So the white plastic is the valve operating correctly.
Or is it only the actuator?

Actuator.

Do I have an electrical problem or a valve problem?

Possibly electrical, but more likely mechanical.

 

[OilLecky]

John,

You first need to get good access to the Diverter Valve. Switch of the electric supply and remove the fuse. remove the screws and move the upper electrical control panel out of the way.
The actuator is fitted to the Diverter valve with a "bayonet fitting." There is a button on the side of the Diverter Valve actuator. Push it inwards and turn the actuator anti-clockwise and then lift it off. Now you can see a pin with a spring around it in the Diverter valve. Get some pliers and gently pull the pin upwards. If it moves then it was stuck and you need to renew the "cartridge". When you buy one you get the special tool to change it as well.
If you now put everything back together and select hot water only (do not select heating!!) then the rads will not heat up. This proves that the diverter valve was sticking if you are still not sure.
To change the cartridge release the system pressure drain a little water out and unscrew the cartridge outer ring which looks like light brown plastic. Fit the new one in reverse order. good luck.

 

[John.Stitch]

Thanks for the advice.
I took the actuator off the top of the valve and did lift the valve stem.
Turing the hot water only the heating remained cold and the water heated up.
So QED.
Looking for a replacement seems to be the thing to do, people comment that the spool may break up on removal, which suggests it is fragile? A bit unusual for it to be fragile.
I am surprised that it breaks up on removal.
I do not have the relevant tool to remove the head of the valve which comes with the replacement.
There is one on the bay for £45.
Or one advertised by abtap for £30.
Or Shoreheat has been suggested.
The Antares catalogue sell for £8.61 but they are not in the UK now?
I could try a plumbers merchants if they stock it?

 

[OilLecky]

Good work Jack.
The cartridge is sticking down in the "heating" position. A common fault.
I buy cartridge elements for about £35, they come with the special tool to remove / fit them. (long nosed pliers will also remove the thing but best to use the proper tool.) My supplier sells the Baxi 241361 cartridge for Worcesters. It's the same thing but cheaper! If the thing breaks up on removal it is no problem. Just remove all the plastic bits and clean out the valve housing as best you can before fitting the new cartridge. Don't overtighten it...it's plastic!

Shouldn't take you much more than half an hour.

With electrical power off and isolated. Drop the system pressure using the PRV (and hope it doesn't leak for ever more after.) Get an old water bowl, and take the pipe off of the Expansion Vessel and about 2 pints of water will drain out. Put an old towel around the diverter valve. Crack the Diverter valve open and catch any water with the towel. You shouldn't get too much out as the system air locks.
Fit the new cartridge.
Refit the actuator.
If you have a pump with a pressure gauge, connect it to the Expansion vessel Schrader valve and make sure that you have the correct air pressure inside. Usually 0.7 to 1.0 bar.
Reconnect the Expansion vessel.
(If you are unsure as to your protection in the heating system add an anti-corrosion treatment via the filling loop connection. Check at a plumbers merchants for this.)
Open the filling loop and raise the pressure at the system gauge to its normal setting (1 bar?)
Check for leaks.
Demand a cup of tea.
If later on the PRV does start leaking and you lose system pressure the PRV can be replaced as easily as the Diverter valve and using the same technique. To determine if your PRV is leaking put a balloon over the outside outlet pipe.

 

[MANDATE]

Why not drop the system pressure by bleeding a radiator rather than risk a problem with the PRV.

 

[oilman]

The PRV should WORK!! It should be checked at every service and not avoided by bleeding somewhere else. If it leaks after, it is defective and needs changing. What would you rather have, the cost of a replacement valve or the cost of damage when a stuck valve fails to operate when needed?

 

[John.Stitch]

Thanks again for the time a trouble you have taken to post to help me.
When I raised and lowered the valve stem I did so a few times to see if that moved any crud.
The valve seems to be operating correctly for the time being,..
A builder advised that the use of the anti scale treatment (if it's the same as the anti corrosion stuff) was pointless in a closed loop system as mine is and it is difficult to get into the system.

 

[oilman]

He's right that it's not much use, but he's wrong as it's a doddle to put in.

 

[John.Stitch]

To resurrect this thread, I replaced the valve in February with a Honeey well replacement.
Recently the problem seems to be recurring with the replacement valve.
I have stripped the old one and cleaned off some black film on the sides of the valve and the valve now moves much more easily.
The black film is probably a mix of grease and water.
I have not regreased any areas as it is mostly plastic with some O rings.
So I will replace the old one and see if that works.
This is a high limescale area so this may affect things. But 10 months is pathetic for a valve.