Baseboard heat knocking when off

Kdizz1820

I’m looking for some help or insight with my baseboard heat in a condo unit. I unfortunately don’t have access to anything beyond my unit, and there are 8 in my section all independently owned. I am on a top end unit. The HOA is kind of useless, so I was hoping someone could give me some info before I reach out to them (if I need to) so I’m better informed.

Normally the knocking sounds are in winter when the heat is in use, which I expect for the most part. However, this one in particular is knocking pretty frequently with the heat off. It is only this one, none of the other sections in my home do this. As far as I can tell there isn’t anywhere that I could bleed air from the line if that’s the culprit. I know some of the fins are bent, but in the winter the knocking is actually less frequent than it is now when the heat is in use.

It is obviously summer, and the heat is not on. Thermostat is turned off/all the way down. When I turn it up I hear the motor engage on what I believe is the zone valve, and disengage when I turn it off, so I don’t believe the issue lies there.

I mostly would just like some input or insight as to what might be causing the knocking now, when the pipes shouldn’t be expanding or contracting, and if there is anything I can do on my end or if it’s likely at the boiler end. Thanks for taking time to read!

leonz

If the boiler also has a domestic hot water coil for the 8 units in this place it would be heating the piping all the time.

Kdizz1820

https://forum.heatinghelp.com/discussion/comment/1804553#Comment_1804553

Oh interesting. I'm not sure if this is the case. I know little about boilers, but I do know that when the heat went out earlier this year because of an issue with the boiler, I still had hot water for domestic use. Not sure if that would indicate they have separate boilers.

I've just never had it knock in the summer or when I have the thermostat off in the time I've lived here and I don't know what would have changed to cause that to start.

EBEBRATT-Ed

When the flooring was done the holes around the pipes should have been larger to account for expansion. Not sure that would account for knocking in the summer at least it shouldn't

You can try cutting up a milk bottle and sliding the plastic around the pipe between the pipe and the floorboards.

hot_rod

In the summer when you hear the noise, is the copper piping under the fin tube getting warm?

If so you may have some ghost flow causing those tubes to warm when they should no be.

You probably need to get access to the mechanical spaces to troubleshoot.

Kdizz1820

https://forum.heatinghelp.com/discussion/comment/1804561#Comment_1804561

It's not warm at all. In the winter the pipes get too hot to touch but right now they're cold. That's why I'm so confused

hot_rod

The domestic hot water piping when someone else in the building is running hot water could be the cause of the noise. Those copper tubes move as they heat and cool also.

EdTheHeaterMan

Depending on the Domestic Hot Water system design, in an 8 unit building, there may be a DHW recirculation loop that has a small pump that operates intermittently in order to charge the hot water pipes so the furthest hot water taps get DHW quickly.  Do you need to wait for a minute or so before you get water after you open the tap?  If Yes then you probably do not have that recirculation  pump.  If you don't wait long then you probably do have the hot water recirculation pump.   That may be where the noise of heating pipe expansion noise is coming from.   

The old design may have non-stop recirculation which may have increased the operating cost of the DHW system.  Someone may have rewired the recirc pump to a more efficient intermittent operation, which will reduce the cost to operate the DHW system. That change may have happened recently to lower operating costs, but it causes the DHW pipes to expand and contract more often.

Another idea is that the recirc pump has failed and now the DHW pipes are allowed to cool off and only heat back up when someone opens a DHW tap somewhere in the building.  

Either way, something has changed and that is where you are getting the new noise.  

So, ask the HOA if there is a Hot Water Recirculation pump on the DHW system and if yes… were there any changes made around the time the noise started to show up?

psb75

It could be a general whole building problem of water-hammer—esp. from thee potable water system. Laundry machine valves, toilets or certain other faucets shutting quickly anywhere else on the plumbing system can transfer the sound (resonance) throughout the building. If it is this, it would not necessarily be a 'seasonal' issue but would be year-round. Water hammer can happen on the heating system as well with zone valves shutting.

CTH3

I installed a DHW circulator because I have an upstairs bathroom that is farthest away from the source. Works perfectly. Sometimes in the morning if I’m awake around 4 AM I will hear the pipes knocking in the summer. In winter it starts before the smart thermostat demands the heat and it is audible and separate from the heat. The noise for the circulator is a knock and not rhythmic as opposed to the baseboard heat which is a tick, tick, tick and rhythmic. Very different sounds.

Adk1guy

I think of times where the pipes were pulled hard through misaligned holes that were too small. When hot water heated the pipes they clunked as they expanded and moved through the framing. When the flow was stopped the pipes clunked as they cooled. If that's the problem its hard fix and may involve going into the ceiling below.