Can I have boiler/central heating leak without a drop in pressure?

frank_olaf

We turned the heating on a few days ago for the first time since Spring and noticed an occasional dripping sound, kind of like water dripping onto plaster board. We an only hear the sound when the heating is on (but it isn't constant), making us think it must be related to the boiler/central heating system. We checked all the radiators and couldn't find a leak so we think it might be a leaking pipe in the walls.

However, the one thing the makes me think it might not be that is the fact that the boiler pressure hasn't dropped. Previously, when we've had central heating leaks (in the radiator) the boiler pressure dropped, so I assume this is always the case.

So, I wanted to check if it is possible for there to be a leak in the central heating system that doesn't affect the boiler pressure? Also, if you think you might know what the issue is, please let me know.

Thanks.

jefaz07

Not if it’s a sealed system. There are caveats to that like a fill loop slightly passing to equalise the pressure reduction due to a leak. 

Is it a condensing boiler? Sounds to me like it’s the condensate dripping while the heating is on. Obviously not seeing the boiler/setup it’s hard to pinpoint. 

That’s my suggestion to start at. 

frank_olaf

jefaz07 said:

Not if it’s a sealed system. There are caveats to that like a fill loop slightly passing to equalise the pressure reduction due to a leak. 

Is it a condensing boiler? Sounds to me like it’s the condensate dripping while the heating is on. Obviously not seeing the boiler/setup it’s hard to pinpoint. 

That’s my suggestion to start at. 

Thanks for your reply. It is a condensing boiler. If it was condensate dripping, could that be anywhere in the central heating system or would that be right by the boiler?
Thanks.

jefaz07

frank_olaf said:

jefaz07 said:

Not if it’s a sealed system. There are caveats to that like a fill loop slightly passing to equalise the pressure reduction due to a leak. 

Is it a condensing boiler? Sounds to me like it’s the condensate dripping while the heating is on. Obviously not seeing the boiler/setup it’s hard to pinpoint. 

That’s my suggestion to start at. 

Thanks for your reply. It is a condensing boiler. If it was condensate dripping, could that be anywhere in the central heating system or would that be right by the boiler?
Thanks.

There will be a plastic pipe coming from the boiler, where this terminates I don’t know (a tundish/washing machine stand pipe) places like that. It may well go outside. Try getting near that to see if the noise is close. 

A boiler won’t ‘condense’ all the time either. So the fact you say it isn’t constant makes me think it’s this.  

Ganga

Are you sure it is not just expansion noise off the pipework.

frank_olaf

Ganga said:

Are you sure it is not just expansion noise off the pipework.

I'm pretty unskilled and uneducated when it coms to DIY so I'm not sure. The sound does make me think it is a dripping sound and my wife thinks so too. Next time I hear it, I'll go into the loft (where the boiler is) and see if I can track down the sound.

jefaz07

If you have an internal soil stack and the condensate is bossed into it then they also could be a place to look. The drop would then fall to the bottom of the stack so if that were the case the noise may actually be coming from a downstairs bathroom? Or near one. 

Again, just guessing. 

Jeepers_Creepers

If this was dripping from a leaking pipe or fitting, then I'd expect it to be pretty constant and steady whilst the CH is on. Also, even tho' it's 'just' a drip, I would expect to see a drop in pressure over a few days - perhaps only a tiny drop, 0.1bar or so - but a drop none the less. 

It is very rare for a drip to only occur when the CH is on. Yes, a dripping leak would likely be greater when the system is hot due to increased pressure and also expanding joints, but I really wouldn't expect a leak to just stop every time the CH is off!

So, I don't think it's a 'leak'. 

What happens intermittently when a boiler is running? The condensate drains. These empty via a small syphon inside the boiler, a bit like a toilet U-bend - and for the same reason; the trapped water acts as a seal to stop smells in the toilet bowl, and to prevent a bad case of death from leaking flue gases in a boiler (in reality it would be that bad - more like a good case of...)

The condensate is actually released from boilers in regular 'glugs' and not as a constant trickle. I think the obvious first step would be to trace the condensate pipe as it exists the boiler, and see where it goes. 

As Ganga also points out, the sound can be very like expansion/contraction noises from a CH pipe which is perhaps clipped too tightly or is rubbing against a joist or similar. As the CH goes on and off, the pipe moves slightly and can 'tick' as it stutters against a surface.

Anyhoo, if you could let us know where the cond pipe goes, that'll help.

frank_olaf

Thanks everyone for the help, I really appreciate it.
The boiler is in the loft and it's hard to see all the piping but I'll go up there this weekend to check it out and try and find the condensate pipe and report back.
Thanks all