Loss of Central Heating Pressure- pipe leak vs faulty boiler

[jimjordan]

Hi

I have a 2 year old (non-combi) boiler in a 50 yr old house with concrete floors downstairs. The system had a leak in one of the heating system pipes feeding the downstairs rads (under the slab) which was diagnosed and fixed by trace and access guys and the system tested clear of leaks earlier this year - since then, over summer, the pressure has been rock steady at 1 bar with the heating off, but hot water on.

Now that the heating is back on again, the pressure is dropping by 0.3-0.7 bar a day (depending how long it's been on for) and needs constantly topping up. Someone has suggested that the boiler might be damaged and is leaking water internally out of the condensation drain and having checked it is indeed passing a lot of water out of that pipe (constant flow of drips when it's running). I asked the engineer who installed/services the boiler and he said it's normal, but the pipes are apparently leak free. So I'm stuck.

The boiler is a Viessmann Vitodens 100.

Any suggestions on how to prove whether the loss is due to the boiler or the rad pipework without dismantling things/capping pipes etc?

Is the fact that pressure only drops when the heating is on but not when the hot water is on relevant?

Is there something I can tell the engineer to do to the boiler over and above a simple annual service that would prove/disprove a boiler fault?

Any pointers would be gratefully received.

 

[Agile]

You can see if the condensate pipe runs when the boiler is off!

It does sound like another leak under the slab.

The boiler can be isolated on its valves for several hours. But if its only leaking when on CH that is unlikely to show anything useful.

Tony

 

[jimjordan]

Thanks - do you know if the CH and HW are separate systems within a typical boiler?

i.e. is the system used to heat the hot water discrete from that used to heat the rads?

Trying to get my head around why the system can maintain 1 bar pressure in the system for months whilst heating water (during which the pressure rises and falls again), but start losing pressure only when the rads are heated.

Would manually turning all of the rads off help diagnosis? They've got thermostatic valves so they've been "off" due to the hot weather.

 

[Agile]

No

No

There is probably a joint under the slab which leaks when hot!

No

 

[jimjordan]

Thanks - that makes sense.