No flow through the first radiator

[Ellya]

Hi,

1970's built 3 bed semi. Baxi boiler and pump working fine.

I had a cold rad in the kitchen (last in the loop) and a cold rad in the master bedroom upstairs (not sure where in the loop). All other rads were working fine.

I drained the kitchen rad and flushed it with clean cold water (there was a fair amount of black sludge). I refitted it and bleed it. I also did the same with the master bedroom rad.

Since turning on the heating again, I get very hot water running up to the TRV on the first rad located halfway up the stairs (The TRV is on the left side). But there is no flow through this rad and All other rads are now cold. I've opened up the valves fully both ends and still no flow. Just hot in the bottom left hand side, cold on the bottom right and slightly warm at the top.

I went around all the rads and bleed them, but there was no air tramped.
I also tried opening up the valves (both ends) on all other rads to see if that helped, but still the same. Just getting very hot water to the first rad halfway up the stairs and all others cold.

Any clues to gettiing the flow going again?

Cheers, Ellya

 

[Softus]

Hi

Hello.

I drained the kitchen rad...

All sounds good, and your description is clear and succinct, but I'm wondering whether you drained the system or just isolated one radiator.

Either way, sometimes the pump can airlock, and will need venting from its vent plug.

I went around all the rads and bleed them, but there was no air tramped.

Nothing tramped, but it could be slut. (Just my little joke).

 

[Ellya]

I just isolated the rads I removed and flushed, not actually drained the whole system, but I think it could probably do with it.

I checked the pump for air, but that was ok, although oddly its mounted on its side, so the vent plug is not actually on the top. It this standard practise or a bodge becuase the main outlet from the boiler is too close to the wall?

Anyway, I noticed at the pump, the parallel out & return supplies are linked with a valve. I shut this down to prevent hot water entering the return pipe and this seemed to get the flow going again. Anyone know what the function of this valve is for?

Cheers, Ellya

 

[Softus]

Your valve is part of a manual bypass circuit, which, in some systems, is an important feature.

Some bypasses are unnecessary; some are vital. If you analyse your system then you'll be able to conclude which of those it is.

Basically, if it's possible for all flow to be stopped by a combination of two-port motorised valves and TRVs, then it's possible for a boiler heat exchanger to be damaged even after the flames go out. In this scenario an open bypass will allow heat to be taken away from the boiler.

If you decide that the bypass valve needs to be open, then open it by about half a turn. Remember that this is difficult to gauge with gate valves, but if the pump is running you'll hear the tone change slightly as some water flows through it.

 

[Ellya]

Thanks, that's good advice. I gave the valve a good half turn and did hear the difference. All the rads still seem to be working now and I've now figured out which order they are from the boiler. I've managed to tweak them (by hand) to get a fair balance too. I have a warm house again!

Cheers, Ellya