Hi,
I'd really appreciate any help so I can try to understand what this issue could be better.
I've read around a lot online but can't find anyone describing a similar issue.
When the boiler starts from cold, there's a large 'thump' from one of the pipes near the boiler (or that's what it sounds like). It literally sounds as if someone has hit a pipe near the boiler with a rubber mallet.
The boiler is a Baxi Solo 3 50 PF, we have a 3-way Honeywell zone-valve and the system is open-vented into a header tank in the loft.
Nothing has changed on the system bar having a Drayon 3-port valve changed for a Honeywell. This only really started about 4-6 weeks after though, so it seems unrelated.
There are no unusual lights showing on the boiler (e.g. overheat, etc). It's turned up relatively high (and I've tried turning it down too).
I've listed the potential points I've looked at below, although none seem obvious culprits (?)
Ignition?
I wouldn't call it a 'thud' or 'boom' or anything that makes it sound like the boiler is slow firing.
It also only happens when the boiler has been left to go cold (e.g. overnight).
There's no smell of gas inside or from the flue.
I've yet to see if there's anything from the flue outside when this happens.
(I may set the boiler to come on later in the morning after we get up at 6 to try and catch it).
Kettling / Limescale?
Although it didn't sounds like kettling, since the house was 15 years old and I wasn't sure how often inhibitor had been used (it seemed so), over Christmas I gave it a clear:
- Drained down, cleaned header tank (joy), and refilled, added F3 for a week, let it run.
- Drained down, refilled, ran water from each lower rad until clear, added F3 to run for a few hours, drained, refilled, ran water from each lower rad until clear, put in F1.
- Each time refilled made sure there were no air locks and all rads bled regularly until all air out.
To be fair, the water was pretty clear (slight tinge) and there was minimal amount of black sludge. The header tank only had about 1mm of black/particles. No foam in the tank or slurry, etc, even with F3 running.
There is no gurgling / sucking / whoosing noises from the pipes/rads.
Running Dry?
I've read sometimes this can be a lack of water in the boiler, often due to a blockage, such as at the water-inlet (from tank to CH system). The header tank fills the system fine. Also when letting water from a drain-down point, it also fills the system fine.
Low Pressure?
Pressure in the rads seem fine. System is balanced and I've re-balanced it a few times to see if it makes a difference. The header tank is in the loft and all rads/parts of the system are below it. Draining from a radiator gives good pressure. All rads get hot.
Air in System?
I'm aware that air in the boiler & pipes can cause the boiler to build pressure & force the air/blockage - which could be likely. That said, there's no air coming from any of the rads, all rads get hot.
Also, this only happens when the boiler is cold - so maybe something is 'settling'/'collecting' over time? (air, slurry?)
When the 3-port valve was replaced, he didn't drain down (according to my wife), but used the isolating valves. That said, I guess *some* air could have got in, but the 3 subsequent drain-downs I've done should have surely shifted any locks..
(again, there's just the thud - no gurgling/bubbling/rushing/sloshing in any rads to suggest air being shunted about)
Blocked Flue or Vent/Outlet
There's a lot online about a blocked, obstructed or iced-up flue causing loud noises on boilder start up. Flue looks fine.
The boiler is on an external wall and vents directly outside through the wall (so flue is likely only 8-12 inches long)
Aggressive Zone Valve
I thought it could be the new zone vale closing/opening quicker/better - as the drayton was slow (first rad would heat up on call for hot water) and would stick in position.
As this sounds near the boiler and only happens when it's cold - I think this is unlikely.
Throughout the day when its coming on/off and the valve will be opening/closing a number of times, it's all fine.
Worn Part / Failure
Some form of part on it's way out? But why would any part function better when warm?
(aside, maybe the ignition. But heating != spark and I'd suspect not any more helpful to helping the boiler light)
Any comments/suggestions appreciated!
(FYI - I'm booking someone to service the boiler and take a look as I won't touch gas appliances, but still want to try and route out the issue as, like most, I'm interested in how things work - and so far, I can't seem to pin this on down.).
Cheers,
I'd really appreciate any help so I can try to understand what this issue could be better.
I've read around a lot online but can't find anyone describing a similar issue.
When the boiler starts from cold, there's a large 'thump' from one of the pipes near the boiler (or that's what it sounds like). It literally sounds as if someone has hit a pipe near the boiler with a rubber mallet.
The boiler is a Baxi Solo 3 50 PF, we have a 3-way Honeywell zone-valve and the system is open-vented into a header tank in the loft.
Nothing has changed on the system bar having a Drayon 3-port valve changed for a Honeywell. This only really started about 4-6 weeks after though, so it seems unrelated.
There are no unusual lights showing on the boiler (e.g. overheat, etc). It's turned up relatively high (and I've tried turning it down too).
I've listed the potential points I've looked at below, although none seem obvious culprits (?)
Ignition?
I wouldn't call it a 'thud' or 'boom' or anything that makes it sound like the boiler is slow firing.
It also only happens when the boiler has been left to go cold (e.g. overnight).
There's no smell of gas inside or from the flue.
I've yet to see if there's anything from the flue outside when this happens.
(I may set the boiler to come on later in the morning after we get up at 6 to try and catch it).
Kettling / Limescale?
Although it didn't sounds like kettling, since the house was 15 years old and I wasn't sure how often inhibitor had been used (it seemed so), over Christmas I gave it a clear:
- Drained down, cleaned header tank (joy), and refilled, added F3 for a week, let it run.
- Drained down, refilled, ran water from each lower rad until clear, added F3 to run for a few hours, drained, refilled, ran water from each lower rad until clear, put in F1.
- Each time refilled made sure there were no air locks and all rads bled regularly until all air out.
To be fair, the water was pretty clear (slight tinge) and there was minimal amount of black sludge. The header tank only had about 1mm of black/particles. No foam in the tank or slurry, etc, even with F3 running.
There is no gurgling / sucking / whoosing noises from the pipes/rads.
Running Dry?
I've read sometimes this can be a lack of water in the boiler, often due to a blockage, such as at the water-inlet (from tank to CH system). The header tank fills the system fine. Also when letting water from a drain-down point, it also fills the system fine.
Low Pressure?
Pressure in the rads seem fine. System is balanced and I've re-balanced it a few times to see if it makes a difference. The header tank is in the loft and all rads/parts of the system are below it. Draining from a radiator gives good pressure. All rads get hot.
Air in System?
I'm aware that air in the boiler & pipes can cause the boiler to build pressure & force the air/blockage - which could be likely. That said, there's no air coming from any of the rads, all rads get hot.
Also, this only happens when the boiler is cold - so maybe something is 'settling'/'collecting' over time? (air, slurry?)
When the 3-port valve was replaced, he didn't drain down (according to my wife), but used the isolating valves. That said, I guess *some* air could have got in, but the 3 subsequent drain-downs I've done should have surely shifted any locks..
(again, there's just the thud - no gurgling/bubbling/rushing/sloshing in any rads to suggest air being shunted about)
Blocked Flue or Vent/Outlet
There's a lot online about a blocked, obstructed or iced-up flue causing loud noises on boilder start up. Flue looks fine.
The boiler is on an external wall and vents directly outside through the wall (so flue is likely only 8-12 inches long)
Aggressive Zone Valve
I thought it could be the new zone vale closing/opening quicker/better - as the drayton was slow (first rad would heat up on call for hot water) and would stick in position.
As this sounds near the boiler and only happens when it's cold - I think this is unlikely.
Throughout the day when its coming on/off and the valve will be opening/closing a number of times, it's all fine.
Worn Part / Failure
Some form of part on it's way out? But why would any part function better when warm?
(aside, maybe the ignition. But heating != spark and I'd suspect not any more helpful to helping the boiler light)
Any comments/suggestions appreciated!
(FYI - I'm booking someone to service the boiler and take a look as I won't touch gas appliances, but still want to try and route out the issue as, like most, I'm interested in how things work - and so far, I can't seem to pin this on down.).
Cheers,
