Why is boiler losing pressure?

[Naomio]

We have a valiant that was manufactured about 10 years ago, but not fitted until 2017. Started having problems the last 18 months with pressure dropping often. Had pump hose replaced, then problem became worse. So were told probably a leak in pipes.

Got out a leak detection specialist who found no leak. The heating was isolated for a few days but boiler pressure dropped. They said it means the problem is with the boiler itself.

Had other engineers go out who can see no fault with the boiler. One is going to fit a new expansion vessel, but said they're not convinced this is the issue because the pressure drops when the heating is off! If that doesn't work what else could it be? Like I said pipes have been checked and rads etc. Help!

 

[Timmy D]

If the heating system was isolated, it can only be the boiler. That is as long as the boiler valves are not letting by. If you want to be 100% certain, drain heating system and disconnect the system from the boiler.

There’s only 3 ways water can leave the boiler.

1. Heating flow/return. Proven by isolating/capping.
2. Pressure discharge. With boiler isolated/not in use, cap discharge off and see if pressure stops dropping. Or tape a bag with tissue in it over the pressure release pipe to check for water.
3. Heat exchanger leak which would allow water down the condense pipework. Bag/tissue it as above.

 

[Ben-gee]

Pound to a penny it’s number 3 in Timmy’s list.

 

[ShaunCorbs]

Prv due to expansion vessel flat is the most common I come across

 

[Timmy D]

If anyone’s interested, came across a HE leak a couple of weeks ago.

 

[Ben-gee]

Prv due to expansion vessel flat is the most common I come across

I agree with this, but as OP has had various engineers look at it I was assuming they would spot this easy fault....
The hex is often harder to spot, more people would miss it.

 

[king of pipes]

I would say it has a internal leak I have seen one like Timmy D,s ,post before and the boiler needed to be replaced , a flue gas analysis would be very very poor has one been done ?? Has it been opened up ?? as below

 

[Naomio]

If the heating system was isolated, it can only be the boiler. That is as long as the boiler valves are not letting by. If you want to be 100% certain, drain heating system and disconnect the system from the boiler.

There’s only 3 ways water can leave the boiler.

1. Heating flow/return. Proven by isolating/capping.
2. Pressure discharge. With boiler isolated/not in use, cap discharge off and see if pressure stops dropping. Or tape a bag with tissue in it over the pressure release pipe to check for water.
3. Heat exchanger leak which would allow water down the condense pipework. Bag/tissue it as above.

This is really useful. We've had 'professionals' out several times, but I'm not convinced they've done this. They just keep on saying they can't see a leak in the boiler and are changing different parts to see if it makes a difference.

When the heating is off the pressure is ok, until the hot water is used. Not sure if that makes any difference, or whether what you've said still applies.

 

[Naomio]

I would say it has a internal leak I have seen one like Timmy D,s ,post before and the boiler needed to be replaced , a flue gas analysis would be very very poor has one been done ?? Has it been opened up ?? as below

Hiya. I'm not sure to be fair. I'll need to enquire.

 

[Timmy D]

This is really useful. We've had 'professionals' out several times, but I'm not convinced they've done this. They just keep on saying they can't see a leak in the boiler and are changing different parts to see if it makes a difference.

When the heating is off the pressure is ok, until the hot water is used. Not sure if that makes any difference, or whether what you've said still applies.

They may have taken the case off the boiler and not seen any leak (so they wouldn’t be lying).
However, with just the case off, you can’t see into the heat exchanger/chamber like in my pics, so they may have missed it.
When you open the HE, you need a new graphite seal kit when closing it back up. This maybe the reason it hasn’t been opened (didn’t have a new seal with them)/potential leak spotted.

It really shouldn’t be too hard to find.

They could also separate the heating system, attach a pressure gauge/pump point and pressurise it to 4 bar. Leave it a day and see if the pressure gauge drops (leak on the system). This doesn’t rule out an additional leak on the boiler as we suspect.

It’s possible that HE leaks only occur when the boiler/HE are hot/in use as the metals can expand/pressure increases.

 

[Naomio]

They may have taken the case off the boiler and not seen any leak (so they wouldn’t be lying).
However, with just the case off, you can’t see into the heat exchanger/chamber like in my pics, so they may have missed it.
When you open the HE, you need a new graphite seal kit when closing it back up. This maybe the reason it hasn’t been opened (didn’t have a new seal with them)/potential leak spotted.

It really shouldn’t be too hard to find.

They could also separate the heating system, attach a pressure gauge/pump point and pressurise it to 4 bar. Leave it a day and see if the pressure gauge drops (leak on the system). This doesn’t rule out an additional leak on the boiler as we suspect.

It’s possible that HE leaks only occur when the boiler/HE are hot/in use as the metals can expand/pressure increases.

Thanks Timmy, you're a star!