Simple explanations for plumbing problems

Water coming from overflow outside house

Depending on the type of heating and hot water system you have this could be a few things. All are easy to diagnose and range from a few pounds to a few hundred pounds.   Follow the easy steps and we’ll find the problem.

1. Look where the overflowing pipe comes out of your house.  Is it from the eaves of the roof, near a bathroom / toilet  or near a boiler/hot water cylinder.

2.Look at the type of pipe the water is coming from what is the material is it metal of plastic.

Plastic pipe from eaves – constant flow

The water level in a tank is too high so it is running out the overflow.  Go into the loft and  take the lid off each tank.  There are normally two but can be virtually any number depending on the size and type of system you have.   Take the lid off each tank and check how high the water level is in each one.

  •  If the ball valve is passing there will be a constant drip on the valve.
  • If the ball float on the end of the valve has split and filled with water the float won’t float so the valve will not shut off.
  • If the coil in the hot water cylinder has burst the water of the heating system and hot water cylinder will try to find their own level.  This will make the lowest of the tanks overflow.
  • If there are thermostatic mixing valves on your hot water system where the cold comes from the mains the non return valve could have stuck open.

Plastic pipe from eaves – only when radiators are hot

Water level in central heating feed tank is too high when cold.

Plastic pipe from eaves – if water hasn’t been used for a while 

Ball valve has a slight leak that isn’t noticeable when water is being drawn off regularly.

Plastic pipe from near bathroom/toilet 

Water level in toilet cistern is too high.  Could be:

  • If the float valve is passing there will be a constant drip on the valve when you take the lid off the toilet cistern.
  • If the float has split and filled with water it won’t float so won’t close the valve fully
  • If the water level has been set too high the valve will never shut and will constantly overfill.

Plastic pipe near a boiler

Could be the condensate pipe from a modern condensing boiler leaking.

Metal pipe near a boiler or hot water tank leaking

This is one of the safety valves opening on the central heating system/unvented cylinder.  The valve opens to release excess pressure from the system.

« What is your problem?

52 responses to “Water coming from overflow outside house

  1. james hunter says:

    water dripping from metal overflow pipe from eaves, but attached to plastic pipe in the loft but only when water is heating hot water tank in loft twice a day! Can u help

    • worgraeme says:

      you need to find out which tank is overflowing.

      if its the big tank that feeds your hot water cylinder it might be that the water level is too high in tank. so when the water heats up and expands the tank overflows. you need to check the ball on the valve isn’t full of water or hasn’t slipped down the arm of the valve allowing the water level to get too high in the tank. The ball valve might also have a slight leak thats just letting the water level get too high.

      • james hunter says:

        thank you very much for getting back to me so quickly, I will have a look and see if its the case as u said my friend, will let u know :-). thank u again!
        james 🙂

  2. Dawn says:

    We have started to have water coming out of our over flow pipe recently? It will all of a sudden start leaking and some times it’s a few drips and other times it’s coming out a lot? Really don’t know what is causing it as were not using the water when it happens? Can you help?

  3. Ciaran H says:

    The water is leaking on and off from a plastic pipe in the eaves. It does it when the heating is both on and off. The heating system has a stove connected with a back boiler. I have checked the two tanks in the loft and they are fine and I don’t think it’s the ball that is the problem.
    Can you give me any advice?

  4. Hannah says:

    I had new kitchen taps fitted but was left with no pressure from the hot water tap. Today a man came to resolve the problem. I now have pressure from the hot tap which is fine but since he’s done whatever he’s done I now have water pissing out from the over flow outside. Can anyone help me or tell me what to do to stop this from continuing. I don’t even know what he’s touched.

    • fixingmy says:

      The 1st step is to have a look at the tanks in the loft. They’ll be wrapped up in insulation. See which one is overflowing. If it is the big one turn off the water to the house. Run a tap until the water level drops then turn the water back on again. The ball valve should shut the water off well below the overflow level (without you interfering with it). If it doesn’t shut off you need to either repair or replace the ball valve.

      • Mattsky says:

        Hey there. How did you fix this? I’m having the same problem – I had no hot water coming from the kitchen tap, I adjusted it so that it did, but when mains water goes back on, the overflow pipe gushes out water. (The water from the top-most pipe in the cold water tank causes the overflow problem.) Any help appreciated.

      • fixingmy says:

        hi, what do you mean by “i adjusted it so it did”?

        The first thing to do is open a hot tap so the ball valve in the tank opens and water starts to go into the tank. Then turn off the hot tap and wait to see if the ball valve closes once the tank is full again. If it doesn’t stop running once the tank is at a level below the overflow (normally white plastic pipe)the fault is with the ball valve.

        If the ball valve shuts off and the water level continues to rise then the fault is normally a mains pressure supply somehow getting into your tank fed system.

  5. Leeanne says:

    Hi, I have two overflow pipes just below the eves that come out via the brick wall. they are next to a bathroom but not a million miles from the two water tanks in the loft. Every now and then we get a big gush of water from just one pipe (and always the same one). I am not sure if there is a link to when the heating is on or now. Its a white pipe so i would assume its plastic. What would you recommend i check first?

  6. Steve Moore says:

    I also have water coming from the overflow plastic pipe but not all the time, I have changed the ball cock several times but the problem keeps coming back. I was beginning to think that it was something to do with the heating system as this is the tank that has the overflow from the heating system, however we went away last weekend so I turned off all the heating but came back to the same dripping issue…. Does this sound like I need a new hot water cylinder as has been suggested to me?

    • fixingmy says:

      If it consistently over flows even when the heating is off there is a good chance its the coil pin holed in the tank. You could try turning the water off over night to see if the water level in the hot water feed tank goes down. Its probably so slow you wouldn’t notice but the water levels in the tanks would eventually get to the same level (big tank lower ,little tank higher).

      The other more rare problem is the cold feed to the system being blocked. If the feed pipe is blocked the water from the system can be pumped over through the swan neck pipe into the feed tank. Its a bit unlikely but can happen just with the hot water being heated up. Try putting the hot water on by itself and watch to see if the water comes out through the swan neck pipe above the little tank.

  7. Louisa says:

    I have identified that the problem in my nan’s house is the below, what can I do about this?

    “Plastic pipe from near bathroom/toilet
    Water level in toilet cistern is too high.
    If the float valve is passing there will be a constant drip on the valve when you take the lid off the toilet cistern.”


    • fixingmy says:

      Sounds like you might need to change the float valve. The first thing to do is hold the ball up and flush the toilet. The water from the cistern will empty into the toilet. Its a bit unlikely but sometimes the float springs a leak and fills up with water. If its full of water it won’t float and will feel heavy. If its full (feels heavy and you can hear water sloshing around) they can be unscrewed and a new one screwed back in. If it isn’t full I normally change the whole valve. You can get kits to change internal washers but for a little bit more you can just get a whole new valve.

  8. Joshua O'Brien says:

    My overflow pipe has a steady flow of water when ever we use any faucet or flush the toilet. We have metal piping in a crawl space under the house. Any ideas as to why and how to fix it would be greatly appreciated.
    Thank you.

    • fixingmy says:

      That sounds like a strange problem. Has the flow of water started recently? Is it particular taps that cause the flow? Without any more information I’m lost with that one.

      • Joshua O'Brien says:

        This occurs when any sort of water is run in the home. No matter hot or cold. It happens when the shower is used, when the toilet is flushed. When any sort of water is used the overflow is pouring water into the crawl space. I’m not sure if this has anything to do with the well or what it could be but while this is happening the pump is making a high pitched howling sound. Hope this helps. If not I’ll be calling an over priced plumber. Thank you.

      • fixingmy says:

        If might be something as simple as a blocked filter. I don’t fully understand how your water system works. But if the pump is howling and an overflow is leaking it might be a blocked filter. If a filter is blocked the pump might be making excessive pressure as it can’t move the water fast enough through the pipework. The overflow that is leaking might be a pressure relief valve opening to release the built up pressure. Its all guess work really. It doesn’t sound like a run of the mill fault so you might have to get some one in.

  9. Jo Buckey says:

    This just might solve my problems, what a brilliant site to have stumbled apon 🙂

    I’ve had a new boiler fitted a week or so ago, and since they fitted it, the plastic pipe near the airing cupboard (and bathroom) has been leaking. They originally couldn’t restart the new boiler and they said the system was ‘air locked’? They then went up into the loft and fiddled around and now I have a leak 😦 I think it might be only when I’m not using water – I went away for the night and came back and it was leaking etc.
    Would appreciate advice before I call the company back as I don’t really know what I’m taking about!
    Thanks in advance Jo

  10. Jenny says:

    the overflow outside is leaking. It is a copper pipe from the boiler. The pressure on the boiler is high 3. I have bled all radiators and the pressure does come down to bar 1-2 but creeps back up to 3. What can I do?

    • fixingmy says:

      The best course of action is always to contact a qualified engineer. But it sounds like water from the cold mains is getting into your heating system when it isn’t supposed to be. The 2 main culprits for this are a filling loop valve passing (or not turned off properly)and the heat exchanger inside the boiler leaking internally.
      The filling loop valve can be checked by turning one or both valves off and removing the silver tube. If water is still coming out of the valve (from the mains) it’s passing and should be changed. Some Worcester boilers have a key in the bottom of the boiler, pull this out to see if water is still flowing. With the silver hose or the white plastic key removed the central heating should be disconnected from the water main so the pressure should stay steady.
      If it carries on rising there’s a good chance the heat exchanger inside the boiler has corroded through and is leaking water from the mains into your ch system. This is a job for a gas safe engineer as its inside the boiler.

  11. Bdog says:

    Do anyone know how to find out where the over flow pipe is outside a house?

    • fixingmy says:

      The best way is to have a look at the thing that might overflow (toilet tank etc) and follow the pipe from it. It will hit an external wall at some point. Go outside your building to roughly the place you’ve been looking at. Now look for a pipe that is similar to the pipe you saw inside the building. That should be your overflow.

  12. joelle says:

    I have a metal pipe and it comes out near the boiler. I use to be a drop but now it is pretty constant. Can you please help? Thank you x

    • fixingmy says:

      Hi Joelle,
      If it’s a combi and if it’s a constant flow it’s usually 1 of 2 things. 1st is the valve that is used to fill the boiler up has been left open (usually by accident) or is passing while it’s closed. Or 2nd a heat exchanger has corroded through and is allowing mains water into the system. Check the valves (usually under the boiler) to see if they have been knocked. You can usually hear the water going through the valves. Either turn the valves back off or you might have to have them replaced. If it’s the heat exchanger you’ll need to get an engineer out.

      If you have a big unvented hot water tank it can be a fault with the air bubble at the top of the tank. The tank will have an explanation printed on the side. Any thing else needs a qualified engineer.

  13. Michelle says:

    Hi need help just had new kitchen fitted the fitters turned water off and when they turned it back on it was gushing out of the over flow pip at back of house help is needed what to do…

  14. Callum says:


    The other day I noticed cold water pouring out of the overflow pipe into my garden (I had the same problem a few years back but with hot water and the landlord replaced the float and the valve). I immediately turned the water off.

    I have looked inside my boiler and I can’t see any dripping from the valve, and the ball float appears to be floating properly. Since I have turned the water back on, no water has been flowing out.

    I’m worried that my landlord is going to say there isn’t a problem and it was just a ‘one off issue’. There is obviously something wrong otherwise the water wouldn’t have poured out in the first place (is that right or could it be a one off?). I just don’t want this to be ignored as it’s going to cost me money if it keeps happening when I’m at work.

    Do you have any idea what the problem could be? Should I get the landlord to bend the arm slightly? Would that work?

    Thanks in advance!!

  15. James says:

    Hi, I have a plastic pipe coming out the side of my house which is right behind where my direct combination tank is placed. The plastic pipe outside has a constant flow of water coming out of it and since the water has been flowing the hot water in the house has not been working.

    Can you please help?

  16. Phily Murphy says:

    Hi, I was wondering if you could shed some light on a continuous problem we’ve been having for years??? Notice the overflow pipe from the attic leaking, climbed up and checked the cold water tank and noticed that the ballcock was no longer working and the tank was constantly filling. Bought a new valve and ballcock and installed, problem was still continuing!!! Got a plumber in who done the same to no effect, told me it was small stones and grit in the mains system that passed the filter and were sticking the float valve!!! We endured this for a while until away overnight and came back to puddles through the attic, into the bedroom below and down through that into my kitchen on the next level!!! Contacted my house insurance company who said they couldn’t help as the cold water tank has to be replaced every 8 years!!! 1st I’d ever heard this!!! Got another plumber in, who replaced the whole system at my expense and the problem still persists, he says the mains in pressure is too high and there’s nothing he can do to remedy that, so we’re managing it at the moment by flushing the loos often enough to keep below the overflow level!!!

    We’re at a massive lose at the moment and would love any info on how to resolve this continuous problem!!! Many thanks.

    • fixingmy says:

      I’ve never heard of the replace every 8 years rule either. Although policies have all sorts of clauses to avoid paying up. If the problem is just high water pressure then there are standard pressure reducing valves available. They are placed in the water pipeline after the stop cock and they reduce the pressure to what ever they are set at, an inline filter before the valve right help as well. It would be interesting to know what the pressure is in the pipes before you do reduce it. Ive checked the pegler website and their float valves are rated to 14 bar which is pretty high.
      For on going overflow problems that can’t be fixed by changing the ball valve I normally look at the hot water cylinder coil being pin holed. Maybe try putting a isolation valve before the problem ball valve so you can confidently turn off the water to the tank. If it still overflows you can be confident its not the ball valve.

      Are all your toilets fed from the tank in the loft? Normally they come from the mains.

  17. James says:

    Hi, I’ve got a problem I was hoping you could help me with. At first I had seen dripping coming from guttering but after I had seen dripping (even when it was a nice hot day outside) I was surprised on closer inspection it was actually coming from a plastic overflow pipe. I had found out it only drips out when the heating is put on and stops when the heating is turned off. I traced the pipe back to the Hot water tank in the loft. I contacted a plumber who said that it was always continuously dripping (whether the heating is on or off) it would be a problem with the ball valve however if it was only doing it when the heating was on then it was due to a problem with the boiler but he would need to come and see it.
    Is that right that it is a problem with a boiler? If I can do something I can do with the hot water tank I’m willing to try but if it’s the boiler there isn’t anything I can do myself. It’s a glow worm ultimate boiler (which is probably 20yrs old) located in the airing cupboard, I’m already worried as when they say “boiler” and “problem” I know its going be expensive!
    Many thanks,

  18. Mark says:

    My overflow pipe only leaks water when I put on the water heating. In my hotpress there is a large cylindrical unit and on the shelf above it there is a smaller unit. Would appreciate any suggestions. Thanks

    • fixingmy says:

      it sounds like the feed tank has its water level set too high. Could be the ball valve starting to pass or the float being damaged. Its worth getting it checked.

  19. Tom Quirke says:

    Well done Worgraeme. My ball cock was full of water in the central heating overflow tank I’ll have to give it a while but for now it looks like you were bang on. Thanks a heap. 😀

  20. Ray says:

    Hello, I have had a new boiler fitted , new cylinder tank, pump yet when the central heating comes on the expansion tank keeps over flowing. My pump is on two which heats the radiators great, but the plumber suggested putting the setting to one which did not heat the radiators properly.Can you please help?

    • fixingmy says:

      The most likely causes are the water level in the tank being set too high or a slight drip on the ball valve. When the heating has been off for a while and is cold check the level of the tank. It should be no more than half way up the tank, any higher and there is no room for expansion when the water heats up. You can adjust the level in the tank either by moving the ball up and down the vertical part of the arm or by bending the arm down a bit. The other reason that comes to mind is the ball valve dripping slightly. It has probably sat for years in the same position and might need to be replaced if its dripping.

      Check the tank when the pump first comes on if water comes out of the open vent (the swan neck pipe pointing into the tank through the lid from above) there could be a restriction in the pipework of the radiators. It might need flushing out.

  21. Lesley says:

    My washing machine caused a surge of water to flow back into pipes in kitchen. Heck of a noise. Very old metal overflow pipe outside kitchen window which has never dripped before is now doing just that. Not good with plumbing. Nothing to be concerned about?

    • fixingmy says:

      get a plumber to have a look at it. If it’s never done it before and you think its linked to a rattling noise it better to have it checked.

  22. Tony Birks says:

    Currently experiencing a problem, where I feel the cold water inlet pressure on a Vaillant ecoTec condensate boiler is slightly too high causing excess pressure to be released via the boiler to an outside pipe. This is constantly dripping heavily

    • fixingmy says:

      The pressure being released out the metal pipe is the water pressure in the central heating system rather that the cold mains. Are both the filling loop taps turned off? Is the pressure high all the time or only when the heating is being used?

  23. Stephen Carmichael says:

    Have a plastic pipe leaking water the pipe is back of house half way up about height of first floor . I dont think it’s over flow for cold water tank as those pipes can be seen near roof. Can it have something to do with the hot water tank which is in a cupboard on landing ?

    • fixingmy says:

      The overflow pipes from the tanks in the loft generally come out at the eaves so it unlikely to be them. I think you might be right about the tank on the landing. It could be that tank or it could be a toilet overflowing. If its the toilet it will be directly connected to the white overflow pipe so should be easy to trace.

  24. Nicola Hart says:

    We have 2 pipes one higher one lower it’s the lower one that is leaking. Any ideas what that would be.

  25. Michael JW Nicholas says:

    Hi, had water coming from a plastic pipe up near the eaves, but only when the beating is on, the tank has water in it sitting an inch below the overflow when the beating is off, what do you recommend? Thanks

    • fixingmy says:

      it sounds like the ball valve is either set too low in the tank (probably because the float isn’t right) or the ball valve is leaking slightly when it is closed. The first thing I always do is change the ball valve.

  26. mbn18201 says:

    Have a plastic pipe up the wall, followed it through into the loft and it’s the overflow to the water free tank, the tank water is very full sits about an inch below the pipe, and water all but pours out of the pup when the hot water is on, what would you recommend as a next step? Eg. Fixed etc

  27. Lisa says:

    Had a busted radiator last week dcc took it off wall came back out new radiator on this morning now I had water coming from pipe out my back

    • fixingmy says:

      Has the filling loop been left open a little bit when he’s filled it up? Check the pressure in the boiler. If it’s high (over 2.5) and the heating isn’t being used then the system is filling when it shouldn’t be. The valve on the filling loop is either closed and passing when it’s closed or gas been left open.

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