combi boiler - fill loop not filling

grumpycrab

Hello - quick question before I get a plumber in... the fill loop for our combi is not working. If I open both fill loop taps no water comes in. It USED to work. So either one of these taps isn't working or this scale inhibitor is blocked (I know there is water in the pipe TO the scale inhibitor).  My question is - can these get blocked?  We have water scale.  Thanks.

ThisIsWeird

Make and model of boiler, please, and pics of filling loop including all taps.

There are likely to be two - are you opening both? Are you sure...?

grumpycrab

Thanks! It's a 3 year old Veissman vitodens 100. We've got very hard water so I'm coming to the conclusion that the inhibitor is blocked.  Filling up, which we'd only done once or twice, used to work. Yes, I'm aware that both taps have to be open. Pic coming...(taps closed)

FreeBear

Two sets of valves there. The black knobs, and the smaller (square) with the slot in. All four are open in that image.

Unlikely the pipe or valves are blocked - You could try slackening off the silver coloured coller and see if water seeps out. Just make sure to have a bucket underneath, and someone manning the stopcock just in case (and have an old towel to hand).

ThisIsWeird

It won't be your descaler, since that supply also feeds the DHW for your boiler - I presume water comes out your hot tap ok?

It's likely that one of these tap fittings has a non-return valve inside it, to prevent 'system' water getting back into your 'clean', so I'm guessing that this valve is stuck closed due to scale - it'll be in the RH tap.

The two brass 'slot' valves are to isolate the boiler from the mains (LH) and CH (RH) respectively, so these are clearly both open or else your system wouldn't work. Then there's the two black taps which are purely for the filling, and - again - both appear to be open, tho' possibly the handles have been put on incorrectly?!

So, don't touch the brass valves, but do try every combination of the blacks; both 'closed'. LH only open. Then close LH and open RH. Turn them all a quarter-turn. Smooth? Any flow?

Finally, if you are up to it, close both, and slowly slacken the two loop end collars. There should only be the briefest of 'pfffts' as the pressure in that wee loop is released, and just a trickle of water which should soon stop. If that's the case, then open fully and remove that loop.

Slowly open the LH black tap, and it should begin to squirt. Don't panic and turn it full on trying to shut it off, 'cos we will laugh.

Then repeat with the RH tap, but bear in mind I don't expect water to come out of this one due to the one-way valve inside.

How to fix? Ye cannae, not without replacing that N-R valve, a quick and simple task for a plumber (or DIYer). Assuming that is the issue.

You could try refitting the loop (do that anyway...), opening the RH black valve fully, and then quickly opening and closing the LH valve, hoping to get a pulse of water pressure to budge the NR valve. Or, open both balck taps fully, and then use summat like a screwdriver handle (firm but soft) to strike the brass body of the RH valve, above where the brass screw is. Tap...tap...tap... If the NR valve releases, then water will immediately flow to your system, so 'strike'...'listen'...'strike'...'listen'...'scream'.

The above is only a guess, of course, but I think the most likely.

grumpycrab

FreeBear said:

Two sets of valves there. The black knobs, and the smaller (hexagonal) with the slot in. All four are open in that image.

That is embarrassing. Makes sense. But I'm totally confused. I need a go-back-in-time button to when it was working.

grumpycrab

ThisIsWeird said:

It won't be your descaler, since that supply also feeds the DHW for your boiler - I presume water comes out your hot tap ok?
... do try every combination of the blacks; both 'closed'. LH only open. Then close LH and open RH. Turn them all a quarter-turn. Smooth? Any flow?

Hot water is ok.  Every combination of blacks tried. No flows. LH is quite stiff.  RH is not stiff at all.

Vortigern

Could the NRV be freed by poking a suitable implement through the RH valve?

ThisIsWeird

Vortigern said:

Could the NRV be freed by poking a suitable implement through the RH valve?

Very possibly, but I wouldn't recommend that to anyone.

ThisIsWeird

grumpycrab said:

ThisIsWeird said:

It won't be your descaler, since that supply also feeds the DHW for your boiler - I presume water comes out your hot tap ok?
... do try every combination of the blacks; both 'closed'. LH only open. Then close LH and open RH. Turn them all a quarter-turn. Smooth? Any flow?

Hot water is ok.  Every combination of blacks tried. No flows. LH is quite stiff.  RH is not stiff at all.

If hot water flow is ok, then your descaler ain't blocked. (These wouldn't suddenly block anyway, but just slooowly build up with scale, with the flow reducing over time - but even that's pretty extreme and unlikely).

Ok, you can safely assume that the two 'brass' valves are 'on'; they look in the 'on' position (slot following flow direction), and your DHW is working, so the LH valve is def open. I presume your CH comes on - your rads heat up - so that means the RH one is also open. And, you haven't actually touched them anyways! So, these are both ON.

The black valves... Chances are that these are 'working' ok too - ie they go on and off. Although one is stiffish, does it still turn through 90o quite positively? And the RH one - smooth and positive? Or does it feel actually 'loose'? Can you tell if the actual valve 'shaft' is also turning as you turn the black handles? Could the plastic handle be slipping on the shaft, and not turning it?

See the screws in the black handles? Ok, watch them closely as you turn the handles thro' 90o - do they turn at exactly the same rate and amount?

  

grumpycrab

ThisIsWeird said:

See the screws in the black handles? Ok, watch them closely as you turn the handles thro' 90o - do they turn at exactly the same rate and amount?

  

They seem ok to me.  The screws follow the handles - full 90o -  LH is stiff and RH one is not stiff - while not loose it doesn't feel like its moving anything.   I'm going to slacken the end collars.