Hi

I have a Vaillant combi about 25 years old. The pressure had dropped and the boiler stopped working so I topped the pressure up via the filling loop. After topping up, the hot water circuit works - although the heat of the water isn't as hot as it had been. When the heating comes on the boiler fires and the rads get luke warm. Then the boiler cuts out. The heating "cycles" with the burner igniting then shutting off after one minute 2 more times. Then an orange light comes on at the front of the boiler next to a "flame" image on the cover of the lower part of the boiler and a sprung button pops out.

I am going to get the boiler seen by hopefully a competent engineer. But forewarned is forearmed. Is this problem probably (possibly) a pump failure on the CH circuit? if yes, how much should I expect to pay (London prices, guv) for a replacement pump?

I accept at some point the boiler will become uneconomic to repair but I am not prepared to junk it if I can get it fixed for a couple of hundred.

Separately, how can a combi lose pressure if there is no leak on the pipes to the radiators nor any water discharged out of the "pressure outlet pipe" (or whatever it is called) out of the back of the boiler?

Thanks

I have bled all the rads and pressurised the system to about 1.5 bar.

On 04/02/2018 18:53, wrote:
Separately, how can a combi lose pressure if there is no leak on the pipes to the radiators nor any water discharged out of the "pressure outlet pipe" (or whatever it is called) out of the back of the boiler?

Leaky joint hidden under the floor or some other obscure place.

On Sunday, 4 February 2018 18:53:37 UTC, wrote:

Hi

I have a Vaillant combi about 25 years old. The pressure had dropped and the boiler stopped working so I topped the pressure up via the filling loop.. After topping up, the hot water circuit works - although the heat of the water isn't as hot as it had been. When the heating comes on the boiler fires and the rads get luke warm. Then the boiler cuts out. The heating "cycles" with the burner igniting then shutting off after one minute 2 more times. Then an orange light comes on at the front of the boiler next to a "flame" image on the cover of the lower part of the boiler and a sprung button pops out.

I am going to get the boiler seen by hopefully a competent engineer. But forewarned is forearmed. Is this problem probably (possibly) a pump failure on the CH circuit? if yes, how much should I expect to pay (London prices, guv) for a replacement pump?

I accept at some point the boiler will become uneconomic to repair but I am not prepared to junk it if I can get it fixed for a couple of hundred.

Separately, how can a combi lose pressure if there is no leak on the pipes to the radiators nor any water discharged out of the "pressure outlet pipe" (or whatever it is called) out of the back of the boiler?

Thanks

it does sound like a pump problem, or possibly crud blocking something. Check the hot pipe coming out of the boiler, if it's poor flow it'll get hot while the rest of the system isn't.

New pumps are about £80 for fancy ones, used unintelligent ones much less. It may just need decrudding or unsticking:
http://wiki.diyfaq.org.uk/index.php/...ng_pump_repair
Also time to look at the filter if it has one.


NT

was thinking very hard :
Separately, how can a combi lose pressure if there is no leak on the pipes to
the radiators nor any water discharged out of the "pressure outlet pipe" (or
whatever it is called) out of the back of the boiler?

You do not need to lose that much water, for the pressure to reduce
below the level. Often the loss can go unnoticed, for years.

Possible sources of leaks, are radiators, radiator valves, pipes and
pipe joints, the expansion vessel having failed possibly causing the
expanded water to be blown out of the over pressure release valve
outside the building, or in fact an internal leak in the boiler itself.
Put a plastic bag over the end of the outlet pipe, to be sure that is
not passing. If a water leak cannot be found with it filled with water,
it can be easier to find with the system drained and pumped up with air
pressure. The noise of (much more) air escaping is easier to trace.