Restarting central heating system

[brian62c]

Just registered and here's my very first post - so hello to anyone reading this!

I'm in the process of putting in a new bathroom and have got as far as installing a fancy new ladder-type towel rail instead of the old rad. I've used the old rad valves (inc a trv) but the trv does not screw in tight - in fact if you keep screwing it in, it eventually clears the thread on the inside!
I've bodged it for now using loads of ptfe and some Plumbers Mait but does anyone know why it doesn't fit properly? I even went to focus and bought a new trv to try and it didn't fit any better so I got a refund.
All suggestions very welcome. The towel rail is from Bathstore by the way, in case that is relevant.
Also, having put the heating and hot water back on, the rads are not yet getting hot after about an hour. I'm assuming they will once the hot water has finished heating (system has been off for 24 hrs plus). Am I right?

Many thanks in anticipation of your combined wisdom

 

[gas4you]

Sounds like this towel rad has parallel 1/2" thread instead of a tapered thread. Shouldn't be a problem, but plumbers mate is not meant for threads, but sink wastes etc

You should feel rads warming up after about 15 mins. Sounds as if you have not filled and vented system properly and have a massive air lock.

Have you checked your pump is working?

What type of heating system do you have?

 

[brian62c]

Sorry Dave, it's the stuff for sealing leaks I've used, not the stuff for bedding in toilets, etc. Sets after about 5 mins. If the offending thread is half inch, why does the lockshield rad valve the other side do up perfectly? Surely both valves are 15mm thread?

I'm no expert but to me system is very conventional, ie non-combi boiler and central heating header tank in loft.
I've been going round bleeding rads but to no great effect. How do you vent the system properly? I thought all you had to do was refill the tank and bleed the rads.
As far as I can tell, both heating and hot water pumps are working (at least their lights are on!). How do I tell if one is not?

Cheers.

B.

 

[gas4you]

Pump lights on two of them? Are you sure you don't mean the lights on your programmer?

This will not prove the pump is spinning, or if you have them, that any zone valves are open as needed.

 

[hi-spec plumbing heating]

threads are 1/2" bsp.

 

[brian62c]

Two pumps - one for hot water, one for heating, as far as I know. Potterton/Myson MSV 222s. Control box is downstairs (I'm not that much of a novice ). When I put my hand on them, can feel them vibrating.
I've just turned hot water off and rads are slowly starting to get hot - and when I looked at the pumps, I remembered where the vent pipe was for the system (I think). It's a vertical bit of pipe about a foot tall next to the hot water tank with a crosshead screwdriver slot in the top. I'm sure that's what the 'real' plumber used after he replaced one of the pumps.

So the towel radiator female threads are half inch as opposed to 15mm are they, hi-spec?

 

[hi-spec plumbing heating]

female or male they are 1/2"bsp

the copper pipe will be 15mm

 

[brian62c]

So the threads on all rad valves - the bits that screw into the radiator/towel rail - are half inch bsp and the end the water pipe connects to is 15mm?

Fair enough, but why then does the lockshield valve from the return side of the towel rail tighten beautifully in the other (flow) side, which the trv was so loose in? And why was the trv I bought in Focus also as loose as a loose thing in the flow side?

And I thought plumbing was simple

 

[hi-spec plumbing heating]

some have a tappered thread so they go nice and tight some don't and seem loose all the way.

but all threads need ptfe tape on them, rad valves useally about 8 wraps.

 

[brian62c]

Okay, thanks hi-spec. I think I'll look for a nice tapered thread trv! Always use plenty of ptfe anyway - in this case about 20 turns!
Thanks for your input.

B.

 

[bengasman]

If it is a straight bsp, you need a different tail. The thread is shorter and they seal on an o-ring. This model is quite rare, most rads are tapered bsp but some e-retailers sell them.
Though the o-ring seal does not need teflon tape, you can put it on if it makes you feel happy.