Rads Problems - Outlets Hot, Inlets Cold

sounds like trv problem
can the heads of the thermostatic valve be removed most unscrew knurled collar under head
if so look at pin underneath head does this move up and down use a coin to press it down
if it doesnt you could try tapping with a hammer on top of pin dont go mad light taps should do it if no joy change valve
sorry if this has been tried just a suggestion

 

have you tried leaving head off trv some times they jam shut in head so when you screw them back they shut it down
yeah they can still let some water thru but not full flow
i would also work the pin up and down a few times just to make sure it releases properly
pushing pin letting it release not with grips you can pull them out by accident
if still the same sounds like pipe blocked
the way your saying about 15mm sounds as if you've got micro bore
are both rads that are affected off same flow and return pipes
you might only have to change them
good plumbers might try looking at which pipe is blocked (flow or return)might be close to valves etc
Once they find which pipe, you can put some pressure thru that pipe to see if it moves blockage

 

AP, checking what Alb says is obviously sensible - tho' you probably already have.

Ie - don't go looking for more complex causes when a stuck 'head' - which is very common - could be the cause (I found one chust yesterday in my own loo - turning the TRV makes fall difference.. ). If the TRV head was stuck half-way down, then it could give you the lukewarm rads when the others are on, and a hot rad with the others off - it would be like a very partially open 'normal' valve. So please try.


How do you know which is the flow and which the return on these rads? Just by the location of the TRV? I hope not.

Anyways, the sixtrilliondollarquestion; has your system always been like this or is it a recent thing?

How old is your system?


Anyways, once you've discounted it being the TRVs or something equally silly, you essentially seem to have a 'sluggish' system; one that 'works', but not at all well (ie - it ain't a complete block.)

So something else you'd likely want to discount is it being a build up of sludge. Any idea if this could be the cause? Did any of the boiler coves test the water for cleanliness or stuff?

Ok, assuming it AIN'T the valves and it AIN'T sludge, then my inclination would be to upgrade the pump. If your pipework is a tad too frictiony to allow a decent flow to all the rads, you can either upgrade the pipe sizes (reduce friction) or increase the pressure to overcome the friction.

Is this a vented boiler with a separate pump? If so, easy-peasy - and you could even pick up a cheap nearly-new pump on t'Bay for testing purposes first.

 

It's a big learning curve .

(If a rad is turned completely off so no flow whatsoever, then feeling the connecting pipes might not give a true idea which is the flow and which the return - the 'return' radiator pipe could well be a shorter pipe so is chust becoming hot from conduction from the nearby main return pipe.

However, if you rad is working even a wee bit, the the 'flow' will always get hotter first.

So, from what you say, the TRVs are connected to the 'returns' on the rads, which is 'ok' if they are bi-directional, but a genuine problem if not. (I'd still personally always fit them to the flows, tho'...)

What happens when they're on the return is that the water exiting the rad tries to push the rubber washer closed, so it can sometimes shut off abruptly before it 'should'. Also, as the TRV tries to open the valve again when the room become chilly, the water pressure can hold the washer shut for longer than it should.

A bi-directional TRV should be able to overcome these issues, of course.

Ok, you are trying the right things; remove the TRV heads, check that the pins can be pushed down smoothly (a thumb will do it but it'll hurt a bit...) and they also pop up cleanly. It should be a 'positive' movement - push down - thunk. Release, pop-up clunk. Ie - firm stopping movement at each end of travel.

With the heads off, do they heat up?

If they still don't heat up as well as they should, first check that it's not because you've left the other rads more open than before, and are therefore stealing the flow. (Or haven't you touched the 'lockshield' ends of the valves?)

Ok, on one of your cool rads, with the TRV head still offski, try opening the lockshield end a half turn (anticlockwise), but note exactly where it was before you start - you must be able to return it to that position afterwards if needed.

See if that makes a difference.

 

Didnt realise youve had work done on system
this could be an air lock, had it before on a system, couple of rads in an extension hadnt worked properly for 6 years , one would be ok or warm other cold then other way round
shut all rads down apart from one of the problem ones
loads o gurggling hay presto scorching rad turned other problem rad on same thing. keep these rads on
turned rest of rads on one by one making sure each one got properly hot before moving to next one
keep the rads on after getting them up to temp
all working great now