Overflow pipe dripping when heating turned on

MillyD123

Hi guys. Any suggestions as to why this might be happening. We have oil central heating and the overflow pipe drips continuously when I switch in the heating.

Thanks in advance

jimf

are your rads / hot water working as normal

MillyD123

jimf wrote: »

are your rads / hot water working as normal

hi Jim. yes all working fine. The water can be scalding though so probably should lower the temperature

Dtp1979

MillyD123 wrote: »

hi Jim. yes all working fine. The water can be scalding though so probably should lower the temperature

Sounds like the ballcock is set too high. Therefore when the heating system is warming up it’s also expanding and raising the water level too high In the attic tank

Maybe worth checking a couple of things, the high temperature of the hot water would be a cause for the hot water cylinder expelling water up into the small header tank and in turn Over flowing.
Perhaps reduce the thermostat and/or the speed of the circulating pump...

MillyD123

Ok thanks for those tips I’ll try them out tomorrow and hopefully solve this.

Paullimerick

Turn down thermostat on the boiler. Also try bending the arm if the ballcock when cold. If it continues after that and the water is still scalding. You may need a new thermostat

Wearb

Rkcorry wrote: »

Maybe worth checking a couple of things, the high temperature of the hot water would be a cause for the hot water cylinder expelling water up into the small header tank and in turn Over flowing.
Perhaps reduce the thermostat and/or the speed of the circulating pump...

Hotwater cylinder doesn't expand into the small tank.

Wearb

Is it an open system? Overflow from where?

MillyD123

Wearb wrote: »

Is it an open system? Overflow from where?

Hi Wearb. It’s open as as I know (open tank in attic). The overflow is coming from this tank and exits just under the eaves

Wearb

MillyD123 wrote: »

Hi Wearb. It’s open as as I know (open tank in attic). The overflow is coming from this tank and exits just under the eaves

Do you have 2 tanks in the attic? Which one is overflowing?

MillyD123

Wearb wrote: »

Do you have 2 tanks in the attic? Which one is overflowing?

Hi Wearb. There are two tanks and it’s the smaller one that is overflowing

Wearb

MillyD123 wrote: »

Hi Wearb. There are two tanks and it’s the smaller one that is overflowing

The previous replies re the ballcock are good then. Just make sure that you know where to turn off the supply before going at it. They are notorious for snapping off when adjusting. Depending on the type, it might be just as handy to replace.

Just something to watch out for is that with plastic expansion tanks, when they get warm, they can become more flexible at the ballcock mounting area allowing it to flex upwards and allow more water than usual in. A bit of bracing would sort that problem out.
An increase in supply pressure (for whatever reason) can cause a problem also, but usually the problem is just wear on the mechanism.

Dtp1979

I have seen on occasion that it’s a pinhole in the coil and only really leaks when the heating is on. Probably in it’s early stages

Wearb

Dtp1979 wrote: »

I have seen on occasion that it’s a pinhole in the coil and only really leaks when the heating is on. Probably in it’s early stages

But I think that would cause the bigger tank to discharge from overflow?

Dtp1979

Wearb wrote: »

But I think that would cause the bigger tank to discharge from overflow?

It depends which is higher. I’m just assuming they’re both on the same base

Paullimerick

The only problem I see with that is that if it has a pinhole and the small tank is lower. It will overflow no matter when.

Dtp1979

Paullimerick wrote: »

The only problem I see with that is that if it has a pinhole and the small tank is lower. It will overflow no matter when.

Not always as I was saying earlier. I’ve seen them leak only when the heating is on

jimf

run off a half bath of hot water with the heating on should show some discolouration if the heating water and domestic water are mixing

unless you have a very clean heating system

some very small leaks will only show when system is under pressure

MillyD123

Thanks for all who suggestions guys. You’ve been very helpful. . I’ll try them all and post back later.

Irish Steve

Could also be that the ballcock has a very slow leak in to the tank due to the washer getting hard, or a small piece of grit in it, so the level is above what it should be.