TRV replacement.

Eldi_Dos

Noticed a bit of leakage on TRV living room radiator, took head off and all seemed fine until pressing the pin down there is a noticable small amount of leakage.

Anyway the plumber is coming to replace the TRV, the question I have is will they need to drain down the whole system to do this? and if so will I need to get them to replace the chemicals in heating system.

WIAWSNB

Eldi_Dos said:

Noticed a bit of leakage on TRV living room radiator, took head off and all seemed fine until pressing the pin down there is a noticable small amount of leakage.

Anyway the plumber is coming to replace the TRV, the question I have is will they need to drain down the whole system to do this? and if so will I need to get them to replace the chemicals in heating system.

If your plumber proposes to replace the whole TRV valve body, then - yes - they'll need to either freeze the pipe to the TRV whilst shutting off the lockshield, or else drain down the whole system, in which case they'd need to replenish the inhibitor. The latter is often the preferred method.

Do you currently have a magnetic filter fitted? If not, please do give consideration to this if 'drain down'. 

bjorn_toby_wilde

Depends. If it’s not a pressurised system it can be changed without draining down. A bung in the header tank…

sheenas

In many case you simply shutdown the lock valves and only loose a small amount of water. You can get them to test and top up the system as required. £10-20 cost tops

Albermarle

sheenas said:

In many case you simply shutdown the lock valves and only loose a small amount of water. You can get them to test and top up the system as required. £10-20 cost tops

Before my last service, I asked how much to test and top up the system with inhibitor- £55 + VAT.
I politely declined.

kassy64

Not a permanent 'fix' but as a temporary measure you may find that by opening the TRV up to highest setting the leak may well stop. I've had this on a few and opening up fully has stopped the leak. only a temporary remedy as i mentioned.

shiraz99

Generally yes, they will need to at least partially drain down the system to replace the valve, however if they're quick they could swap the valve over without as long as the system has been depressurised. There's a few vids on YT showing this done.

Eldi_Dos

WIAWSNB said:

Eldi_Dos said:

Noticed a bit of leakage on TRV living room radiator, took head off and all seemed fine until pressing the pin down there is a noticable small amount of leakage.

Anyway the plumber is coming to replace the TRV, the question I have is will they need to drain down the whole system to do this? and if so will I need to get them to replace the chemicals in heating system.

Do you currently have a magnetic filter fitted? If not, please do give consideration to this if 'drain down'. 

Yeah got a magnetic filter in place.

The plumber had look at TRV, boiler and location of stopcock, so has information needed to do job, he is on standby this week so said he will pop round sometime during the week, workload depending.

Eldi_Dos

bjorn_toby_wilde said:

Depends. If it’s not a pressurised system it can be changed without draining down. A bung in the header tank…

 thanks:
It is a combi boiler, so no header tank, I was just curious about which approach he will use.

Eldi_Dos

@kassy64

When I took the head off the valve (which it still is) the leak stops only when pressing pin down can you see slight seepage.

WIAWSNB

With a sealed system, there is surprisingly little water loss. 
The boiler itself is the part which 'stores' the pressure in an EV. So usually it's boiler off, CH isolating valves shut off underneath it (they might not bother), bleed a rad until no water comes out, slacken valve and drain rad, and then quick swap with only a wee further glug coming out the tail. 
This is because air needs to get in that pipe end, for water to come out. The gentlest of finger presses over the end will stop the air/water exchange.
A tray and towels should capture any dribble.
I wonder if plumbers have their own particular technique?! Please report back with how they do this!