Another mid position valve problem

[Andrew453]

Hello


I'd be grateful for some help with an issue with my heating/hot water system please.


The mid-position valve, while it will move under the power of the actuator does not move the full extent of its range. Therefore, when on hot water only, it doesn't quite make it to the end of its travel such the the heating gets some hot water too and the radiators become hot. The central heating and hot water both work fine as far as I can tell - it's running them independently that's the problem.


There's some history to it:


1) The heating was last powerflushed in 2009 and treated with inhibitor.


2) I've had trouble with the actuator before, and replaced that. I've never replaced the valve itself, so it's at least 10 years old.


3) Recently, I had trouble with the mid position valve again. I thought it was the actuator, but when I dissassembled it I found that the valve itself had actually seized. I managed to free it up without removing it using some pliers, and it would travel the full extent of its range. The heating/hot water system worked fine for a bit.


4) A few weeks' later I noticed the present problem.


5) My hunch is that it's sludged/scaled up inside. If I move the valve down (i.e. towards mid position) with the manual lever on the side of the MPV and then pull it up again (i.e. towards hot water only), I can get the valve to move further to the end of its travel, but then there's a minor clunk from the boiler and it springs back a bit. (Naot sure if there's any significance to that behaviour).


6) I went up into the loft to check the H/E tank. It's very sludgy. The water itself is clear (or at least it was until I disturbed it), but there's about 5mm of sludge at the bottom. It has roughly the consistency and colour of a muddy puddle. I'm in a hard water area.


For various reasons, I really don't want to have to replace the valve if I don't have to. (Access is really really poor).


Here's my plan:


a) Fish all the sludge out the H/E tank.


b) Drain the system (without tying up the ball cock) until the exit water runs clear.


c) Tie up the ball cock, and drain until dry.


d) Exercise the valve to try to free it up.


e) Refill, adding Sentinel X200 and X100 (descaler and inhibitor).


f) Bleed etc.


g) Hope for the best.


My question is whether the X200 is likely to be effective enough to desludge/descale the valve and whether the above approach is the right one, at least initially. I'm not quite sure how the X200 works, given that you don't drain the system afterwards. Presumably, it just breaks the material down and it floats around forever more.


I imagine I'll end up having to pay someone to replace the valve if the above doesn't work, but given it's £30 for the chemicals versus £300 to replace the valve, I think it's worth a punt in the first instance.


Any advice welcome. Thank you.

 

[gassafe]

You need to replace the valve body already

 

[gassafe]

I'm not sure where you got to the 300 pound figure to replace the valve

 

[ShaunCorbs]

As above you need to replace the whole valve

 

[Andrew453]

Thank you. How much should that be to do?

 

[TVP&H Ltd]

Put a location up and someone here can give you a better idea of price...!

 

[Andrew453]

I'm near Amersham, Bucks. Thanks.

 

[Masood]

Thank you. How much should that be to do?

You've said access is tight so it really does depend on how tight. Normally not even an hour's work for a competent plumber.

 

[lame plumber]

You've said access is tight so it really does depend on how tight. Normally not even an hour's work for a competent plumber.

if it is accessible, not seized up, drain offs work etc etc etc. has taken me all day before now, even involved removing cyl to get at the bleedin thing, no such thing as an easy job, 5 minute wonder etc etc

 

[Andrew453]

Yes, quite. That's what I'm worried about.

I appreciate the healthy scepticism re whether what I'm suggesting will work (and no doubt it'll come to pass that it needs replacing) but the worse case seems to me that I take the approach in my first post but it doesn't fix it, in which case I'm £30 down. I managed to free up the MPV again, so suspect it's sludge/scale.

On the assumption that I'm not going to replace the MVP in the first instance, has anyone got any suggestions or comments on the questions in my first post please?

 

[ShaunCorbs]

Yes, quite. That's what I'm worried about.

I appreciate the healthy scepticism re whether what I'm suggesting will work (and no doubt it'll come to pass that it needs replacing) but the worse case seems to me that I take the approach in my first post but it doesn't fix it, in which case I'm £30 down. I managed to free up the MPV again, so suspect it's sludge/scale.

On the assumption that I'm not going to replace the MVP in the first instance, has anyone got any suggestions or comments on the questions in my first post please?

how do you know the internal flapper is working and not snapped from when it seized ? best to change the whole lot

 

[Andrew453]

Because when I move it, it moves only from one extreme to the other, doesn't go all the way round and diverts the water in the right directions.

 

[Chalked]

Hi
You will need to replace the valve body. I know your looking for a reason to not, but you will waste your money.
Depending on which make of valve it will still burn out another motor. You. cant choose where the cleaner will work and most valves get stiff where it passes through the body, so cleaning won't help.

 

[Masood]

if it is accessible, not seized up, drain offs work etc etc etc. has taken me all day before now, even involved removing cyl to get at the bleedin thing, no such thing as an easy job, 5 minute wonder etc etc

Exactly why I mentioned the access! No need to drain though, bung it and move fast... 😀

 

[lame plumber]

Because when I move it, it moves only from one extreme to the other, doesn't go all the way round and diverts the water in the right directions.

that is what they are supposed to do!!! they dont twirl round in circles

 

[Andrew453]

Yes exactly. I was responding to ShaunCorbs question as to how I know it's working.

 

[jtsplumbing]

The area you are in is very hard water, when you had P/Flush did they do a de-scale at same time ? you need a better quality de-scale'r in your system I would be looking to use Kemco's own brand or Fernox But Kemco do very good chemicals.

 

[Simon 45]

Hi
I had a similar problem last winter, I left the valve in and changed the workings, I should say I had a spare mid position valve, I found the fault it was a sticking micro switch I repaired it and keeping it as a spare.
You will a need an electrician to carry out the repair.

 

[Riley]

Hi
I had a similar problem last winter, I left the valve in and changed the workings, I should say I had a spare mid position valve, I found the fault it was a sticking micro switch I repaired it and keeping it as a spare.
You will a need an electrician to carry out the repair.

Or a competent heating engineer