New combi boiler & dripping overflow - are they related?

CraigS46

Hi, this is a bit of weird one (or at least I think it is - maybe it's not to an expert).

We recently replaced our system boiler with a combi.  At the same time we drained and capped off the cold water tank and removed the hot water cylinder from the airing cupboard.  

The replacement itself brought it's share of troubles - when draining the cold water tank they flooded my daughters bedroom for one thing - but now the issue we're seeing is that the overflow pipe in the eaves (I assume from the cold water tank) is dripping fairly consistently during the day.  

It's not a rush of water but just a steady drip every minute or so - sometimes it stops for hours at a time then starts up again.  

The combi boiler has also dropped it's pressure down to under 0.5 in less than the 2 weeks we've had it fitted.

I just can't see how the overflow pipe can be dripping - I've been up into the loft and both the cold water tank and expansion tanks are still bone dry.... so where is the water coming from?  

I can only think that somehow the central heating pipes which still run into the loft from where the hot water cyclinder sat are still connected somehow to the cold water pipes and into the overflow????    Is the overflow drip somehow related to the combi losing it's pressure so quickly?

I'm at a complete loss - the guys who fitted it are coming back out but to be honest they didn't exactly fill us with confidence first time round, at one point they couldn't get any hot water and they asked us if we knew why it might be!

thanks for any thoughts/input.

grumbler

There are two overflow pipes - for the cold water tank and for the CH expansion tank. Both have to be disused now and can be removed. Both can be tracked easily - either do this or ignore dripping.

I guess the boiler is installed not in the loft - it has its own pressure relief valve and corresponding pipe.

nofoollikeold

1. Could be a WC cistern overflowing.  If previously tank fed but now on the mains, pressure may be too high.
If WC, have a look in the cistern.  If there is a red cone in the fill valve (low pressure), this should be changed for a white cone (high pressure).  Not all inlet valves have these cones, so may be more practical to change the whole inlet valve.
2. Installers should have at least warned of this possibility, or better still, have made necessary modifications.  
3. Pressure drop could be caused by air in revised system.  Get pressure back to normal (around 1.2 bar) and keep an eye on it.  Re-pressurising by a few points of a bar every 6 months is acceptable.  Any more, then get the installers back.

CraigS46

nofoollikeold said:

1. Could be a WC cistern overflowing.  If previously tank fed but now on the mains, pressure may be too high.
If WC, have a look in the cistern.  If there is a red cone in the fill valve (low pressure), this should be changed for a white cone (high pressure).  Not all inlet valves have these cones, so may be more practical to change the whole inlet valve.

Thanks, I was afraid someone would suggest this - we got the bathroom done a couple of years ago and it's all tiled in
I'll bear this in mind for when the installers come back, cheers.

nofoollikeold

If the bathroom is only two years old it is most likely there will be an internal overflow, in which case it won't be what I suggested.

Jeepers_Creepers

Don't panic, Craig - if it's a faulty cistern, you won't have to rip up any tiles

Is this overflow pipe definitely coming from the loft? You sure...?