Vaillant VCW 221 H no CH. DHW fine

[walerah]

Hi. I've read through a few related posts and gather this is quite an oldie (and theres quite a few vaillant smarties on here) but I can't afford to replace just right now.

VCW 221 H - PROBLEM : pictures of microswitch + 'stuck' return spring

hot water works fine, demand, click sound, green + amber light on, boiler fires, pump on, hot water.

Central heating:no click, no green+amber, boiler doesn't fire, pump on.

2 years ago BG did a fix price jobbie, similar fault then but they replaced auto air vent, Circulation Pump and Expansion Vessel CH - seemed to sort it out.

last year had problem with pilot light going out intermittently so I replaced thermocouple.

both CH and DHW working fine through winter 07 but CH off since, past few weeks tried to get CH and it wont work.

manually poking microswitch behind servo triggers green then amber light and fires boiler but only for a few minutes.

desperate to see if it's a diy fix before winter kicks in, got a quote from BG 210 pounds

all help appreciated, got an electric heater on standy as theres a kid in the house - will bite the bullet and pay if it can't be fixed

other info:
-room thermostat clicks on/off at around 22c
-there appears to be some minor calcification on some pipes below servo.
-also water pressue unstable, increases intermittently from 1 bar up to 3
-thermostat on boiler is not working so can't get any temps if that's an
issue

vcw 221

• walerah
• 11 Oct 2008
• 1

ch/dhw off. actuating arm is at rest leftwards top switch is adjusted not to engage, bottom...

vcw 221

• walerah
• 11 Oct 2008
• 2

dhw/ch on. actuating arm moves outwards (right) clears both micro switches

vcw 221

• walerah
• 11 Oct 2008
• 1

servo? spring return on the back remains in same position on or off ch/dhw

 

[Rob]

Make sure the spring in the third pic has fully retracted after HW demand has finished.

 

[mickyg]

As he says above, best way to check is to push down on lever as in pic so spring depresses as shown.

Untitled

• mickyg
• 12 Oct 2008
• 2

see if heating works as you hold this down, if so probably faulty water valve. You can adjust the pin sometimes to overcome problem, but the valve will prob need replacing sometime soon.

 

[walerah]

As he says above, best way to check is to push down on lever as in pic so spring depresses as shown.

Untitled

• mickyg
• 12 Oct 2008
• 2

see if heating works as you hold this down, if so probably faulty water valve. You can adjust the pin sometimes to overcome problem, but the valve will prob need replacing sometime soon.

thanks guys.

it seems the opposite case. the spring cannot compress any further than shown in the picture. the black lever (cam?) can be pushed in the opposite (left) direction forcing the spring to stretch and the cam to push the microswitch [this DOES activate the CH but only for a few minutes]

any further direction appreciated.

2 side notes guys:
the push rod below the cam appears stuck(?) and at no point (ch/dhw) is it raised or lowered.

the 2 microswitches to the right of the boiler - the top one is never engaged? should this be? I ask cos one of the final steps in the manufacturers fault finding manual for the diverter valve says "check actuating lever is correctly adjusted to actuate both micro switches" this does not appear to be the case with mine, does this need to be adjusted?

 

[superdupergasman]

The cam that you are looking at is the DHW actuator. Pin should come out as tap is turned, pushing cam upto Left and makes red micro switch.

This can be adjusted but if it does not move at all then I would suspect thats this is faulty also, although I have not worked on these boilers much.

 

[spacethegas]

i would check if the expansion vessel is sufficiently charged re the pressure rising.

regarding your ch problem. its worth you taking a look at another active thread as it applies to you too.

//www.diynot.com/forums/viewtopic.php?t=151738

the middle picture is right for dhw calling.

both those microswitches should be depressed when ch only is calling.

 

[walerah]

i would check if the expansion vessel is sufficiently charged re the pressure rising.

regarding your ch problem. its worth you taking a look at another active thread as it applies to you too.

//www.diynot.com/forums/viewtopic.php?t=151738

the middle picture is right for dhw calling.

both those microswitches should be depressed when ch only is calling.

thanks for the link spacethegas, looked promising but mines slightly different. re both microswitches being depressed, why would the top switch not be depressed when CH only is calling?

I noticed the lower arm is spring loaded and perhaps requires more pressure 'from somewhere' to it to depress leftwards enough to allow the top arm to push the microswitch... i dunno

can this 'lack of extra pressure' on the lower arm be linked to the servo valve not being engaged due to the push rod not being raised to make the microswitch behind the servo? I noticed this so I dropped the water section

water valve

• walerah
• 12 Oct 2008
• 1

the 'pin' appears stuck and withdrawn and heavily calcified

could all of this lead to the pressure being raised unintentionaly?

lastly follwing the manual I attempted to clean the water section and have a look at the diaphram but 2 of the 5 screws are rusted/fused and wont budge, sprayed Wd40 to loosen no luck, tried carefully to unscrew but the slot is wearing away so I may have to buy a new water section (if that proves to be the fault)

 

[spacethegas]

you said you get hw.
so the pin on the water section must travel out when the hot tap is opened in order to move the cam to operate the microswitch.

diverter microswitches

boiler off- top micro out. bottom micro made.

hw on- both micros out.

ch on- both micros made.

the servo valve & those little tubes make that happen.

 

[Gasguru]

This lot normally gets them working fully......

Re-charge the expansion vessel as per FAQs. It's a fiddle getting the pump onto the schrader valve on these boilers. It's also normal for a small initial quantity of water to drain from the vessel. If the pressure has reached 3 bar (or near) you may find the safety valve has opened...so check for leakage.

Tapping the screws with a hammer can sometimes free the threads. A cordless drill (impact driver even better) can also help free them. Good quality pump pliers on the screw periphery normally shifts them.

If you can get it apart replace the diaphragm and stuffing gland...clean the pin and the insides thoroughly (de-scaler?).

Check the adjustable operating pin is free to move...sometimes the plastic sleeve becomes ccontaminated and swells.

Pop off the spring and check the cam operates freely...sometimes leakage on the O ring seal prevents full return. Unless you know the condition of the servo valve you may want to consider replacing it. I have stripped them down and cleaned them up sucessfully. The tiniest amount of muck can prevent operation since the device consists of two ceramic discs (similar to a 1/4 turn tap). Different ports are lined up in each posistion to revese the control pressure on the diverter diaphragm.

Mark each control tube before removing them and clean out each one. One tube connects with a banjo bolt onto the diverter. Check the bolt...if it has a pin/disc/retainer inside discard these parts, otherwise just check it's clear. Check the drillings where the tubes connect are also clear.

The diverter internal parts could be partially seized or the diaphragm weak...assume it's ok for now though.

Adjust the pin above the water section and microswitch position as per the manual....easier if you pull forward the control box (but make sure you re-connect the air hoses at the back).

Replace the auto air vent unless you are sure it works. Disconnect the connection at the pump and pull the connecting pipe out complete with vent.

Re-fill the system, open up the combustion chamber and you will see another bleed point on the LHS of the heat exchanger. Thoroughly check the condition of the combustion cover seal and re-secure. Make sure it is fitted correctly.

Shut off the gas and run the boiler in heating mode. Open the hot tap every so often to help purge the air into the rad circuit. You may have to turn the boiler off/on to bypass the anticycling timer and help air clear through the aav when the pump stops.

When the boiler appears quiet from air turn on the gas.

If it still doesn't work diverter and pump are the next items to strip and check.

 

[walerah]

you said you get hw.
so the pin on the water section must travel out when the hot tap is opened in order to move the cam to operate the microswitch.

diverter microswitches

boiler off- top micro out. bottom micro made.

hw on- both micros out.

ch on- both micros made.

the servo valve & those little tubes make that happen.

to be honest I always had the HW off when walking through the fault finder so I hadn't realised the cam made the MS on HW demand.

anyway I seem to have got the CH working ...for now. the top micro now makes on CH where it didn't before - ever, apparently the bottom micro sort of makes in 2 stages on phase 2 the spring on the lower arm compresses further leftward to make the top micro.

gasguru thanks for the massive rundown. fortunately the air vent, and pump were replaced by BG about 18 months ago. I tapped the screws, even put a lighter flame for a few seconds under the 2 corroded ones, no joy, I did still immerse the water valve in descaler, stripped the servo, it appeared to have a rusty film, used a soft brush, checked the spring, cam was moving freely, descaled and lubricated the push rod behind the servo, re assembled and it fired up nicely. the upper micro made for the first time.

so everything works for tonight though I'm not sure where the problem was? servo or water section. tempted to order a spare water section as the stuck screws mean I've been unable to look at the diaphragm which I gather is important to replace on a boiler this old.

i'll have a look at recharging the epansion vessel tomorrow, let you guys know if i need a hand with that.

appreciate all your help guys - legends every one

 

[Agile]

If the pin is moving on a DHW demand then there is no point in changing the diaphragm.

Its odd but they rarely fail on older vaillant boilers.

If you wanted to invest in a tool the remove stubbon screws you could buy an electric impact driver.

Look at:-

http://www.screwfix.com/prods/98740/Power-Tools/Cordless-Drills/Sparky-GUR12-12V-Impact-Driver

Tony

 

[walerah]

thanks for the tip Agile, I do have an impact drill though my concern was that the problem screws happened the two that didn't go straight through? (ie 3 of 5 are visible from both sides and the stuck 2 appear to terminate within the body of the water valve) anyway I'd imagine it easier to drill and pick out the debris if I was drilling straigh through. but that's for another day.

to help me understand what happen (should it happen soon again) before I stripped the servo and descaled the water valve replaced some broken washers the microswitch showed a delayed and sluggish response to DHW and CH demand and when demand stopped it held for a while and then slowly depressed so the lower micro made and the upper micro didn't.

after: the micros react smartly on demand and return smartly both micros being made when DHW is stopped.

given all my symptoms and pictures is any of you able to put a finger on the exact part that makes this possible.

I'm worried the present working state may be a fluke and would like to be sure the steps I took are directly linked to the upper micro now making.

also Agile, where's the best place to source replacement screws for the water valve ie is there a code or measurement to google? as they are not everyday screws.

 

[Gasguru]

Impact driver for the screws or gas axe at kwik-fit.

Don't worry about what happened..it's often a combination of several minor faults....each device needs to work properly.

 

[namsag]

99% of faults on these used to be caused by either the water section pin not returning properly due to scale or the servo valve was faulty , air in little bundy tubes can be a pain to get out after draining , but i never had a faulty divertor on these even though fault finding charts used to lead you there

 

[spacethegas]

99% of faults on these used to be caused by either the water section pin not returning properly due to scale or the servo valve was faulty , air in little bundy tubes can be a pain to get out after draining , but i never had a faulty divertor on these even though fault finding charts used to lead you there

i have worked extensively on these & i also have never seen a faulty diverter.