Postby rachieroo » Tue Sep 08, 2009 7:13 pm


I could really do with some help, I know that this problem has been posted so many times before but unfortunately seeing as my degree wasn't in central heating I really don't understand!! :D

We moved into our house last yr and not long after water started overflowing from a pipe just under our roof into the garden (trust me, any terminology more complex than that and I'm lost). My fiance went in the attic to check and apparantly we have two tanks, and the little one was overflowing. At the time we did not really notice any pattern to it but changed the ballvalve (is that right?) and its washer and it seemed to do the trick.

Up until approx 2-3 months ago it started happening again, ballvalve is fine this time, but it seemed to be usually around early evening which i can only think corresponds to our hot water coming on, as its been summer our heating hasnt been on at all. My dad knows a fair bit about central heating systems and my uncle is an ex gas engineer so we had pretty good advice from them who both suspected that the problem lay with the hot water cylinder and maybe its thermostat. Seeing as we had cover from Swalec they advised us to ask them to come out instead of us paying again to get it sorted. The man from Swalec came last week and to be honest he seemed to have as much of a clue as I had and was quite happy to change the ballvalve until i told him that I had already done it. I told him that I heard my fiance mention that the pipe leading into the tank was boiling hot which seemed to trigger a eureka moment and he scuttled off to have a look at my airing cupboard. He didn't even touch the cylinder turned a pump down from 3 to 2 and said if it carried on the only other possible thing it could be is, and i quote, "a blocked cold feed". He said the only way that can be fixed is to obviously find the blockage, get rid of it and then we would have to pay 4 to 500 quid to have it powerflushed otherwise they wont cover it.

Needless to say the damn thing started playing up again tonight and now i'm in a bit of a conundrum as what to do. My dad and uncle recoiled in horror at what the man said and have come up with all sorts of explanations instead of a blocked cold feed which as you can probably tell I wouldnt understand.

Is there anybody who can give me some plausible explanations as to whats going on in small and simple words and whether or not I should brace myself to remortgage the house to pay for it if Swalec have to come back lol.

Thanks for reading this!!
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Joined: Tue Sep 08, 2009 6:45 pm


Simply Build It

Postby plumbbob » Wed Sep 09, 2009 11:50 am

First of all, let's ignore anything the Swalec engineer has contributed because although he has diagnosed a fault, I believe he is barking up the wrong tree and anything he has suggested could very well be simply misleading with respect to the problem you have.

If the small central heating header tank is over filling to a point where it overflows, then extra water must be getting in somewhere. In fact, there are only two ways this can happen. If we discount the ballcock because it has been replaced the only other way is, and you are not going to like it, through a pin hole in the hot water cylinder coil. Why this is worse when the hot water is on is beyond me - maybe it's to do with expansion? Anyway, it's not relevant. The point is because the DHW header tank is larger and the water level higher than the small heating tank the higher pressure is forcing water from one circuit across in to the heating circuit.

Unfortunately, the only solution is a replacement cylinder. Ouch!
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Postby rachieroo » Thu Sep 10, 2009 7:03 am

Thanks for the advice, I seem to understand that. After looking through some of the other queries on here to the same problem, I thought you would say that, to be honest I'm not too bothered about changing the cylinder because I have scoured every single page of my contract with Swalec and nowhere does it say that changing a cylinder is not covered, it even has a big tick next to it on the "what's covered" list....but if anyone who has central heating cover with Swalec knows otherwise please let me know!!! The only way I suppose they would get around that is by saying that the reason it split in the first place was down to limescale build up etc (is that a possible reason) in which case I'll have to see if I can get it done cheaper elsewhere. They also said that if it was the cold feed blocked, they would change the blocked part under the cover, but they wouldn't cover me unless I had a power flush afterwards so maybe they will do that.
The only thing I thought of last night that could contribute to the problem is that my heating system is designed slightly differently in that the airing cupboard and therefore cylinder etc is downstairs basically where your under the stairs cupboard and I've noticed that at least 3 other houses in the street have overflow probs at the mo, maybe I'ts a design fault, or just coincidince due to the fact our cylinders are likely to be the same age?
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Joined: Tue Sep 08, 2009 6:45 pm

Postby rachieroo » Sat Sep 12, 2009 4:45 pm

well Swalec came back today when I was in work and it was the same engineer, told my fiance before he even got through the door that it was definitely a blocked cold feed. My fiance asked him over and over if he was sure as by now we have had 3 other ppl including the reply on here saying a split or hole in the coil in the cylinder. He was adamant so when he told him about the possibility of the cylinder problem, he dismissed it straight away saying our water would be dirty. We told him we want a second opinion so a diff engineer is going to come and have a chat to us, and we think we'll get someone other than swalec to have a look too....will let you know what happens
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Joined: Tue Sep 08, 2009 6:45 pm

Postby aidie » Thu Sep 17, 2009 11:47 am

I assume when you said "the pipe leading into the tank" your talking about the system open vent pipe i.e. the one that terminates back over the top of the tank.
Basis first, as you have change the ballcock make sure it is not set to high, you only need around 150mm of water in the tank when the system is cold, this allows for any expansion before it reaches the overflow pipe, if there is a gap between the water level and the overflow pipe when the system is in use "hot" it sound like the open vent is flowing back up and over into the tank, check the recirculation pump setting, and adjust to setting to 1.
If it's been working in the past with out any trouble! make sure the tank water level is not to dosen't need much to start the open vent overflowing back into the tank.
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Joined: Thu Sep 17, 2009 11:23 am

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