Hammering in CH system

[docboardman]

Hi everyone.

We have completely refurbished our CH system. There is a new condensing system boiler, all new pipework, new rads and TRVs. We haven't installed a programmable thermostat yet, but that will happen in due course.

I have noticed that sometimes, after the CH system has been on and at a stable temp for a while, there is a low level humming noise coming from the system. If I put my hand on any of the pipes coming from the boiler, they are vibrating. This is also true of the pipes around where the CH valve is.

All the rads have been bled, but this has not cured the problem. Sometimes if I turn the system temperature down, the humming eventually stops. I can also make it stop if I open all of the TRVs to full or if I open the valve for the HW system (we have an S plan).

I recently became aware that TRVs are normally put on the flow pipe, but I'm not sure all of the ones on our systems were installed that way.

Does anyone have any ideas about what might be going on or how I could further diagnose this problem?

Cheers!

 

[Armo74]

has a bypass valve been fitted into the system pipework as some boiler manufactures request

 

[docboardman]

Hi Armo74. Yup, there is a bypass valve. There is also one rad that has no TRV on it and it's always wide open. It's located where the thermostat will be.

 

[Armo74]

was the system flushed after installation as that could result in system noise. if so i can only think that it is possibly down to having no room stat yet and the only device telling the boiler and pump that temperature is satisfied is the boiler stat and all your trvs are closing leaving the water still pumping round the system however a bypass usually takes care of pumping against a dead head. I would install roomstat asap because under current regs you should have one and see if that takes care of it. Any more experianced tradesmen please feel free to correct me as i am new to this.

 

[Armo74]

In response to your question about the trvs on flow or return most new trvs are bi-directional so being on flow or return shouldnt matter. The system should have been flushed after installation sorry for repeating that but did not think i wrote it clear in last reply.

 

[Armo74]

The reason i suggested about the the room stat is because you say the noise goes if you fully open trvs possibly leaving the water to flow through while the boiler stat has been satisfied before the trvs are closed because they are on max. sorry for so many messages should have written it all in one

 

[docboardman]

Hi Armo74 -

Good point about flushing the system. No, we didn't. I am still working on the house and we are just about to finish the last bedroom. I have another rad to hang there so it might be a good time to just take a breather, flush out everything and clean the whole system. At least we will know where we are then.

There will also be two CH towel rails to put in, but I haven't started on the bathrooms yet. I'm not sure they will have TRVs. I don't know if that would help with the problem. In other words, there would be a bypass plus two rads to take the flow when all the TRVs have shut down.

Come to think of it, the rad in the room where the thermostat will be has no TRV. So it is always on and should act as a bypass. Isn't that right, or am I missing something?

In any case, I've been lazy about the thermostat. I know the one I want and just haven't made the time to go get it. I'll get on to that now.

Thanks for the info on positioning the TRVs. I was worried that they should be on the flow and not the return.

Cheers for now. I'll try to post the result when we get the thermostat installed.

 

[Armo74]

If you are thinking of using the bathroom rads as a bypass i would advise you put trvs on them otherwise in the summer when you dont need heating but you do need hot water you wont be able to control the temperature in the bathroom as you only really need them on low to dry your towels. You should not put a trv in the same room as your room stat as they just work against each other. Two locksheilds should do the job.

 

[docboardman]

II see, that's true. I hadn't thought of that. In fact, we were going to make the towel rads dual fuel and run them off electricity in the summer. I think that means you close them off from the main CH system anyway. So that means they wouldn't be suitable for a bypass ... at least not in the summer.

The rad in the room where the thermostat is has no TRV on it. Does that not effectively make it a bypass? If not, there is a bypass built in to where the valves for CH and DHW are.

 

[Homesafe]

Yes a rad with lockshields on and with a set flow rate going through it is in theory a by-pass.

 

[herebriefly]

Hi Armo74 -

Good point about flushing the system. No, we didn't.

Your poor new shiny boiler aint gonna last long then

Your vague on system betails... Y or S plan? What is the new boiler... apart from white? I understand its a system boiler.

Have you done all this work yourself? Was the system chemically cleansed or powerflushed in accordance with MI's? I assume you have not just fitted a boiler to a untreated system and the fact you have not flushed it yet means the chemicals are still in and your flushing all the chemicals out when the works complete. Still a bad move IMO.

I have noticed that sometimes, after the CH system has been on and at a stable temp for a while, there is a low level humming noise coming from the system

You already have crap in you new boilers heat exchanger.

David.

 

[docboardman]

Hi David, and thanks for your response.

In my first post I said it was an "S" plan, but maybe I didn't make it clear.

The details are:

Worcester Bosch Greenstar 24i system boiler.
DHW comes from a thermal store made by DPS (www.heatweb.com).
The thermal store has a bypass fitted to it.
There is also an "S" plan valve system fitted to the thermal store.
Every inch of the plumbing is new copper pipe.
There are Honeywell TRVs on all the radiators except the one in the room where the thermostat will be.
All work has been done by a professional CORGI registered plumber with about 40 yrs of experience.
I assumed that we didn't flush it because everything was new. Perhaps this was an oversight by my plumber. I guess swarf could have got into the system during construction, so we'll have to address this.
The system was drained and refilled about at least once because of a problem we had during the construction (not related to the CH plumbing).
I had a Worcester Bosch factory technician service the boiler last summer under warrantee. It got a clean bill of health.

Hope that answers most of your questions.

We have one more radiator to put onto the system now since we've finished work in the last bedroom. I talked things over with the plumber (including the hammering) and we're going to completely flush the system now. We'll also look at all the TRVs to make sure they are in good order.

At the end of all that, I'll come back with what we find and if that fixes the hammering.

Cheers and thanks for your help!