Hot Water / Heating / overflow problem

[theukmoog]

This started a couple of weeks ago but I've been away and this morning was the first chance I've had to investigate.

One of the 2 overflow pipes has been dripping onto the patio of a morning, starting soon after the heating/hotwater comes on and stopping soon after the timer ends.

It's coming from the smaller of the two tanks in the loft... I've lifted the lid to have a look inside in this picture...

and inside looks like this...

I was expecting the problem to be the float valve, as I had to replace the float valve in the bigger tank last summer when it started constantly dripping, leading to a constant overflow drip.

This time, it's the small tank (heating/hot water expansion tank?) and it's not the float valve - that turns off completely - but rather the pipe coming into the tank from above is pumping hot water into the tank when the heating/hot water system is on. The water in the tank was quite warm and causing condensation on the outside of the cold water tank next to it.

I have a memory of looking inside this tank when I replaced the other float valve and the water level was nowhere near the top/overflow then (last summer).

We've lived here for over 3y and it has only started this behaviour in the last couple of weeks.

Before I call a plumber out... any idea what's causing it?

Thanks for any advice

 

[Werewolf]

IIRC that smaller tank is normally the header for the central heating, basically allows for the central heating water to have somewhere to go when it expands if it's not a combi boiler, and allows it to automatically top up if say you bleed the radiators (modern combi boilers use a sealed expansion vessel to allow for the expansion, and a manual feed tap under the boiler to do the job of the float valve).

I'm not a plumber but it might indicate there is air/a blockage in the heating pipes causing the water to back up when the circulation pump is running.

Basically it's for the radiators, so go round and check for any signs of cold radiators to give you an idea if there is a blockage.