Cold Radiators

[enfopaul]

I have a convential boiler with 12 radiators connected. During the summer months we were decorating downstairs which involved moving the positions of 2 of the radiators.

For routing pipework reasons, the existing pipe work (flow & return) were cut off and capped.

To provide hot water to the radiators in their new positions, I tee'd off an existing branch that supplied the bathroom radiator. I then tee'd off this again to provide hot water to each of the 2 radiators. The same was done to provide the return flow.

The system has been fully drained and refilled (along with inhibitor). Now when I turn on the central heating all rads work except the 2 new rads (The pipes feeding and returning to each rad is cold.)

I have done the following to try and cure the problem.

1) Bled air from all the radiators over a period of a couple of days, where present.

2) Bled off about 2 gallons of water from the problem radiators (via bleed nipple) incase of an air lock on the radiators.

3) Turned off all radiators except the problem ones to try and force the hot water to pass through.


Most radiators, including the new radiators have TRV (universal flow). The 2 radiators that were moved were replaced with brand new radiators (and brand new TRV's and lockshield valves).
If I unscrew the TRV and draw water off - eventually the feed pipe gets hot but the radiator only gets luke warm at the top and cold at the bottom. The return flow at best gets only lukewarm. (i have tried fully opening the lockshield valve in this state but no improvements).

Once the heating is turned off again, the problem goes back to cold feed and return pipes on the 2 new radiators.

Any ideas as what to try next

 

[Bahco]

To provide hot water to the radiators I tee'd off an existing branch that supplied the bathroom radiator. I then tee'd off this again to provide hot water to each of the 2 radiators. The same was done to provide the return flow.

Think you need to repipe as you may be asking too much of how you have fed them. Balance them too.

 

[Timmyturtle]

Just a thought ...The bathroom rad is off the heating circuit and not the primaries?
ie.the rads work when hot water is selected

 

[enfopaul]

Think you need to repipe as you may be asking too much of how you have fed them. Balance them too

. :

Bahco - this had crossed my mind but I've been in denial about this possibility

Is there a rule of thumb that can be used to determine how many radiators you can feed as a spur? I guess in an ideal world every radiator would branch from a 22mm pipe central pipe and deliver the run to /from each radiator in 15mm?

If I have fed too many rads from one pipe - would they still not get hot when I turned all the other 10 rads off When I did this I took off the TRV sensor head and fully opened the LSV.

Thanks for your help so far.

 

[enfopaul]

Just a thought ...The bathroom rad is off the heating circuit and not the primaries?
ie.the rads work when hot water is selected

Hi Timmyturtle.

If i understand your question - you are asking have I fed the 2 moved rads from the hot water system

To confirm the, the programmer has 2 modes: HW only and HW & CH. Setting to either of these modes doesn't change a thing with these 2 rads.

After I had put in the new pipes for the 2 moved rads, I took the rads off until recently. When I drained down the system last weeked to put back the new rads, I drained from the drain cock and also drained the excess water from the new pipes as I hadn't fitted any drain cocks there (tut, tut ).

When draining water from the flow and return - the water stopped coming fairly quickly - therefore - I think that this also backs up that the pipes were connected to the CH circuit and not the HW circuit otherwise the water would have kept flowing for ages whilst the hot water storage tank,etc had emptied

 

[enfopaul]

Does anyone think it might be a good idea to turn off the valves at both sides of the problem rads, drain the radiators and then open each valve in turn to check for a positive flow from both sides.

Even though the problem rads are brand new, is it worth flushing them through whilst there off as well to ensure now blockages - is it a false assertion to say that the rads should be fine as they are new

 

[Bahco]

Lots of people with rad problems just lately.

I shall refer them all to this post