Potterton Puma 80 radiators not hot

[radio_engineer]

HI,

Had plenty or problems with boiler to date. Boiler is Puma 80 and problem is that radiators are not getting hot but HW is fine. I have searched this forum and used my own tests to conclude that likely problem is vax capsule diverter valve. This is what occurs.

DHW is fine but it comes out very hot to start with, you could burn yourself almost.

When boiler in CH mode, it fires up and then flames go high then reduce as expected but after relatively short while they stop. Pump works all along. Under boiler CH pipes get warm (hot after while). It appears to me flow of CH water is restricted. I have warmed up diverter valve capsule with hot air gun. this improves the flow of hot water to radiators but after while the flow slows down.

I have today drained system, flushed it with cold mains, filled with system cleaner in case there are some particles blocking the valve seat.

Can diverter valve be taken apart and only vax capsule changed? if so any place one could get capsule in NW London ( around Park Royal NW10)
Is it worth changing capsule only? Can I test capsule to see if it works?

Is there any other explanation to problems with this Puma? Pump was changed about 2 years ago and since then flow was not best. Is it possible I have fitted the pump wrong way round the arrow on the pump body point upward toward the heat exchanger. There is bypass valve under boiler. Should this valve be closed to improve flow? anf if so by how much i.e. shut or half closed.

Sorry for to many questions.

 

[Slugbabydotcom]

Can diverter valve be taken apart and only wax capsule changed?

Good question! The answer is no unless someone else knows something I don't. Its amazing the things you can find out on this forum.

This is a better question:-

There is bypass valve under boiler. Should this valve be closed to improve flow? anf if so by how much i.e. shut or half closed.

Just cracked open usually.

You got me with this one

Is it possible I have fitted the pump wrong way round the arrow on the pump body point upward toward the heat exchanger.

I cant remember... Maybe someone else can help with this bit.
I dont suppose you will still have the old one kicking about? Dust usually lands on the top of them! I am sure that when you fitted the pump you will have taken note of its orientation and the way the wire went into it.

 

[ChrisR]

Yes you can buy just the capsule and change it, but you're inclined to get leaks. I'd say change the whole thing, as the other part may also be dirty etc. Not a long job.

Try removing the wax capsule to clean it. You undo that very "thin" plug on the end, 24mm I think.

The pump should pump upwards, ie with the lump on the back at the bottom.

Remember pumps can be going slow (common on old pumas now) , be clogged up, or the rotors can be loose.

It's hard to diagnose between pump and DV or a CH blockage. The hw works well without the pump even running!

 

[radio_engineer]

Hi,

If I change the whole valve do I need to have access from back? I mean do you mean I remove four pipe connectors two 15mm and two 22mm or just two 15mm. There are some small hex screws holding what looks like one section?

I have seen valve on internet and it has tread on the back?

 

[corgiman]

thats the flow to the rads

also there is a back nut back there that is a swine to undo

good luck

 

[radio_engineer]

Yes you can buy just the capsule and change it, but you're inclined to get leaks. I'd say change the whole thing, as the other part may also be dirty etc. Not a long job.

Try removing the wax capsule to clean it. You undo that very "thin" plug on the end, 24mm I think.

If I change capsule only as described above do I need to drain CH water out or only HW ?

As boiler is boxed in to get to back nut on diverter valve I need to remove some wall ceramic tiles also !!! Is there any trick to change this valve without easy access to behind bottom connectors? Hence reason I am inclined to only change capsule if it can be done from the front.

thanks for help

 

[ChrisR]

you wont buy capule alone easily.

you need to at least take pressure off to remove capsule.

30mm rear nut is easy only with wierd tools or goood access.

you wld also need new 1/2 & 3/4 washers

While drained remove pump head and ceck torque. Shld be hard to stop withone finger.

check pump cap, they dry up. 1.5uF iirc.

Flat on back in the corpse factory, hard to use these dangly keypads!

 

[Slugbabydotcom]

Is there any trick to change this valve without easy access to behind bottom connectors?

The more access you can get to it the better. Sometimes it would be easier to take a boiler off a wall for such a repair.

Heres some tips that may be useful

Theres a rather useless bit of plate held in with a couple of screws. Its probably there for a purpose. Few people know what this purpose is and I am not one of the few so I usually hoy it. This makes access to the 'b*st**d nut on the back' a little easier.
Get the wd40 on it ASAP
Tapping the nut round the thread with an hammer and old flat screwdriver can often help in getting it off as well.
Dont use cheap or old knackered tools if you like the skin that covers your hands.

 

[ChrisR]

Once the rear pipe connection's off you can get a socket on "that " nut.

 

[radio_engineer]

I have purchased new wax diverter valve assembly. Instead of replacing the hole valve I have decided to take front section off the new valve. This is held by 2 small hex holding screws. This way only 2 of the pipes at the front will need disconnecting. The new front part of the valve fits the old housing. I have cleaned area inside the old part so that O ring seals well.

It appears the repair was success, the hot water is back on and radiatiors are hot also. No leaks inside boiler.

The only down side is that after I have refilled boiler there is some noise in the system. It sounds like some particles in the system but it could be air also. For information system was flushed with cold mains feed and then system cleaner was added.

What is the best way to purge the system from air?. I have vented all radiators and have opened small screw on the water pump front till some water had come out. There was hardly any water going out of the pump so perhaps this should be repeated.

Thanks all for your help I am happy now. job done!!

 

[ChrisR]

I think you took the best route.
The "particles" which sound like gravel ARE air, and will find their way out.
There's an auto air vent top left of the boiler which should have a loose cap. They often leak and need replacing.
Fun to reach with a spanner - release the lhs of the boiler case if there's room.