Combi-boiler problems

[RussP]

When our combi-boiler is off the water pressure drops so much that the boiler is not able to ignite. When the boiler is on the pressure go up and we are able to get hot water and hot radiators. We are constantly needing to top up the water in the system so that the pressure is sufficient for the boiler to start. Does anyone know what might be the problem, before I call in the experts?

 

[miah]

I'm not a Plumber or an expert in this fields but I read something similar in the past.

Possible cause....

If It's constant then it may be you have leak somewhere or it may an expansion vessel failure.

 

[blueshields]

How long does it last when topped up 1 hour, 1 week ?

If you are losing pressure over a longer period and you are getting losts of air/hydrogen when you bleed the rads, you might have lots of sludge in your system.

If you are losing pressure over a short period, check if the pressure relief valve is drip. If dripping while cold it is probably scaled up, if dripping while hot, you probably need the pressure vessel charging.

Do you have any leaks from Rad valves etc ?

 

[ollski]

fill the system cold to the pressure specified in the manufacturer's instructions. just one question though....if the boiler won't ignite how does the pressure go up when it's on?

If you constantly need to top up the water you must be losing it from somewhere...this could be anywhere, rads, pressure relief, expansion chamber, pipework.

 

[RussP]

How long does it last when topped up 1 hour, 1 week ?

If you are losing pressure over a longer period and you are getting losts of air/hydrogen when you bleed the rads, you might have lots of sludge in your system.

If you are losing pressure over a short period, check if the pressure relief valve is drip. If dripping while cold it is probably scaled up, if dripping while hot, you probably need the pressure vessel charging.

Do you have any leaks from Rad valves etc ?

After topping up, it only lasts an hour or two, if the system is not on. No leaks from the Rad valves, have bled the rads, nothing too abnormal there. Wondered about scale build up though.... Thanks for your prompt reply.

 

[blueshields]

After topping up, it only lasts an hour or two, if the system is not on. No leaks from the Rad valves, have bled the rads, nothing too abnormal there. Wondered about scale build up though.... Thanks for your prompt reply.

Like I said, check the PRV. Should be a pipe runnig from the boiler outside or into a tundish.
Water must be leaking from somewhere.
The scale/crud I mentioned would be keeping the PRV open and letting water open.

 

[RussP]

fill the system cold to the pressure specified in the manufacturer's instructions. just one question though....if the boiler won't ignite how does the pressure go up when it's on?

If you constantly need to top up the water you must be losing it from somewhere...this could be anywhere, rads, pressure relief, expansion chamber, pipework.

Sorry I think that I need to clarify; I top up the system to the manufacturer's specified pressure, and then turn the boiler on to constant. However, when it is on a timer, and not on, the pressure goes down within 2-3hrs. I don't actually ignite, as the boiler turns it's self on, but is unable to heat up and just make a lot of noise trying. It's not coming out of the rads, so I guess it could be any of the other places that you have mentioned. Thanks for your prompt reply.

 

[miah]

Please read the following quotes, there not my words though.

I Hope this helps.

“problem it is that when the system over presuurised the Pressure Relief Valve opened, quite rightly, but has failed to close off correctly due to a bit of muck or the sealing washer being corroded”.


“ If the drop never happened before then a system leak is very unlikely but it won't hurt to inject some leak sealer “

 

[ChrisR]

CHECK THE PRESSURE RELIEF VALVE PIPE!!!!!!!!