Broken screw on heater control valve - what to do now

[Rbatt]

I have been investigating my lack of cabin heating. I decided to replace the heater control valve o ring today.

Unfortunately, I have broken off the screw on the top of the control valve. The valve is stuck closed and I cannot now use a long screw to lift the valve upwards.

The metal indicator piece on top of the valve is firmly stuck onto the brass valve and I cannot remove it (or indeed twist it to turn the valve to the open position).

I have tried to twist this metal indicator clockwise with pliers but I'm worried about damaging the copper housing as it is very stuck.

Any ideas on what I can do now?

1967 230SL
 

[Rolf-Dieter ✝︎]

I think you need some expert help here, someone with the right tools.

There is a shop in the London UK area (see below) Give him a call or drop him a line. Go to his web site www.colinferns.com for contact info.

Good Luck

Dieter

I added some links below that may help you out.

Some help here ---> https://www.kmstools.com/blog/removing-broken-seized-fasteners/

or here ----> https://www.youtube.com/watch?v=0iyJtGNemq4

 

[Rbatt]

Thank you for your reply. I think that I will be able to get the broken screw out/ retap a new screw or even change the heater control valve. But first I have to get the valve out. I won't budge.

Has anyone on here had a similar issue with the valve (and metal indicator guide) stuck? What did you do?

[Benz Dr.]

I've repaired quite a few of these things and every repair tends to be a bit different than the one before but I'll give you general ideas. You will need to have the air scoop off and all the parts below it to the point that you can see the heater flaps and heater core.

Once this valve is really stuck it can be very difficult to remove. Sometimes I try to tap it down slightly with a punch so that it breaks the bond between the valve and the outer casing. Once I move it down, I sometimes use a long screw and thread it through a number of small washers placed on top of the casing so that the screw can thread into the hole in the top of the valve. By turning the screw and changing the number of washers used I can sometimes get it to work like a gear puller. Regardless of method, limiting the amount of force is critical. As you have already found out, the screw can break off and then you're ( pardon the pun ) screwed.

Once you are able to get the valve to move even a small amount it will usually come out. Polish the valve so that it will fit into the heater core without binding. I use liquid silicone to lube the valve which also makes the O-ring on the valve work much better.
 
Mark the angles ( fully open and closed based on where the hole is pointing ) on the top of the valve as it opens and closes ( this is important ) so that you can determine where it's pointing to as you try to index the valve. I concentrate on making sure it's fully closed when the heater lever is off so that there's not any heat for summer use. If it's set up right, you should be able to get very warm heat when it's fully on. You may have to take the screw back out and move the valve one position on the square of the valve ( left or right ) so that all of the linkage works properly when open or closed. 

It's not the job from hell but it's pretty close sometimes. Oh, and don't be surprised if you drop that little piece that slots into the casing that indexes the valve. I have many times and you won't find it either. Best to place some rags or something like that around the core to prevent that from happening.

 

[Tyler S]

Another thing you can try is to remove the heater hose that feeds the valve and insert a slightly bent screwdriver into the heater core and gently tap on the valve to break it loose. This screwdriver also helps when re-installing the valve so you don't push it down too far and loose it inside the heater core.

When I pulled my leaking heater core to replace it, amongst the air box I found $1.27 in change, 3 bobby pins, a thumb tack, several tooth picks, a really old heinz ketchup packet, postage stamps, an earring, several screws, and 2 of those heater valve indexing tabs!

[catjim813]

Rbatt,  if all else fails I have an extra control valve, keep us posted how it goes. 

[ja17]

Get the engine and coolant good and hot first. It can help quite a bit. Next remove the hose in the engine bay that connects to the valve. Spray penetrant inside the valve once the hose is removed. Also spray penetrant on top the valve. I also like to tap down on the valve first to break things loose. Do not tap down too far. The valve will eventually fall into the heater core and disappear forever.