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Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 8432
Experience:  Retired mech. contractor, shop owner, 51 yrs experience.
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Strange problem, recently had a pipe repaired due to a leak,

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Strange problem, recently had a pipe repaired due to a leak, since then no hot radiators downstairs, hot radiators upstairs, hot water is ok everywhere, the hot water only setting on the boiler seems to heat up the upstairs rads, whats going on?
Welcome to Just Answer!

There is air trapped in the system, it entered when the leak was repaired. You need to bleed the radiators in the zone with no heat. Use the tiny air bleeds near the top of the radiators... bleed until just a tiny squirt of water comes out.

Run the system for a while, then bleed them again, if the radiators upstairs stop heating bleed them too.... air tends to migrate in the system.

If you cannot find the air bleeds send me a photo of the radiators or a good verbal description, we can go from there.... as long as you rate my responses positively I will hold the question open.


Phil and other Plumbing Specialists are ready to help you
Customer: replied 4 years ago.

Thanks for your advice, I've already bled the radiators twice, its the entire downstairs that isn't getting any heat. The pipe that heads downstairs and connects to the mid point valve seems far colder than the other pipes in the system, would this matter?

Hello again,

If the system worked before the leak repair and not after the leak repair, it is almost certainly an air in the system problem....


- The plumber may have closed a valve and failed to open it again.

- or changed the piping in some way, for instance changed it so there is an
inverted U in the loop going to the downstairs... that would trap air and unless
he put a vent in the top of it, you would not be able to bleed the air out.

Tell more about the leak and what was done to repair it... and the details of how you bled the air... did the water squirt out under pressure, or barely come out of the bleed valves.

That pipe that heads downstairs is colder than the other pipes because there is no hot water flow in it....trapped will cause no water.. not much else will if the system worked before.

Tell me in detail about how you did the bleeding downstairs, did much air come out, did much water come out, were any valves left closed?

We can go from there until we get this figured out.

Customer: replied 4 years ago.

Thanks for such a fast reply.


The repair was to a pressure outlet pipe connecting to the Mid valve, which had bent was leaking, the plumber replaced and soldered the pipe, it doesnt leak anymore. We had to drain both the hot water and the CH system before making repair, which we did from the lowest point in the house.


After we switched the water back on I was given instruction to bleed the radiators, which I did, some radiators had high pressure pretty quickly (within a few moments of twisting the bleed key) others took longer, but water was coming out of all them with reasonable pressure eventually.


After which me and my neighbour who came over to help diagnose the issue ran the heating system set to the highest temperature for an hour, all the upstairs radiators were very warm, the downstairs rads were very cold. Then we checked the downstairs radiators by bleeding them while the system was running and the water in them was cold.


We tried draining the system again, and repeated the process above to see if there was air in the system. The problem still occurs.


An interesting side affect is if I set the water to auto and the radiators to off, the radiator nearest the boiler still comes on. And the hot water pump seems to come on for hours, infact it's not turned itself off yet today without me turning the system off.


Hello again, there may have been a mistake selecting or fitting the mid valve..

If you can send me a picture by using the *paper clip link in this dialog box or by sending the pictures to[email protected] attention 'alumalite', that will help

Meantime re-bleed all of the radiators again, two or three times if necessary *but do not drain the system again, each time the system is drained a lot of air gets into it.


If that fails:

I need some photo's and brand and model numbers on the item you are 'setting the water to auto' on...

.... and I need to ask you to feel the motorized valves that open the hot water flow to each radiator or zone upstairs... tell me how warm it is, compared to the same valve(s) for the downstairs.

It could be that the valves are not opening on the down stairs system.

We can go from there

Customer: replied 4 years ago.

Here are the pictures you requested, we only have one mid point valve in the system.




The system is set to auto from the controller next to the boiler, this is a danfoss fp715

Hello again, thanks for the photo's.

Judging by the solder job you photographed the valve might be installed upside down by a novice plumber.

If the valve is closed, the pipe attached to port A (marked on the valve will be closed and the pipe from port A cool.

if its open, to the mid position all pipes will be warm more or less.


Tell me please if the label on the front of the old valve was upside down as this one appears to be or not.

Let me know what you find regarding port A and the valve position, we can go from there until the situation resolves.


Next steps if necessary will involve operating the valve manually and checking power to the valve and watching it operate and noticing the temperature at port A pipe and connection.


Customer: replied 4 years ago.

the valve itself was not changed, merely the pipe was resoldered as seen in picture 2.


the valve switch moves automatically depending on if the radiators are on, and can't be moved to the left by hand, it moves over to the left if the radiators are turned off automatically.

Hello again.

it sounds like the valve is working ... that leaves us with air in the system. Are there any electric control valves at each radiator? If so, tell me if the ones upstairs have warmer valve controllers on them than the ones downstairs.

(there a hundred different ways these systems can be controlled, I have to ask about the details in each case)

Let me know, we can go from there

Customer: replied 4 years ago.

each radiator has a manual valve that can be opened or closed with pliers, (all are open) and a temperature setting ranging from anti frost to 10. All are set to 10.


Even though we have instant hot water, the water pump is still running almost 24/7 (I've had to shut it off at night, this is different to before the repair was made)

Hello again,

the leak repair should have had no effect on the pump run cycle, however if the pump is operating off of A pressure switch, air in the pump cavity itself could cause it to fail to reach its shut off pressure. You might try looking on the pump head for an air bleed, or an 1/8" pipe plug, then shut of valves on each side of the pump if you can find any, and loosen the plug, until it wiggles...if there is any air in the pump cavity it will come out.

BE SURE TO TURN OFF THE CITY WATER SUPPLY TO THE BOILER BEFORE LOOSENING THE PLUG. tell me if this boiler is being operated with the city water make up valve open, or if the system is sealed and the city water make up valve is only open on start up..or to re pressurize the boiler.

Tell me what the pressure gage on the boiler reads, and if water barely blows out the boilers pressure relief valve when you lift the lever, or it blows out with some force... we want the boiler pressure to be between 15 and 25 psig.

Tell me if air comes out of the pressure relief valve when you lift its manual release handle.

There is not much else besides air in the system or low boiler pressure in a sealed system (make up water valve closed) that will cause these sorts of problems.

Customer: replied 4 years ago.

The system is connected to a cold water supply from the city via a main valve in the garage. As far as I'm aware, the system only takes water from the mains to replace water thats used by taps etc. The lowest drain points are auxillary pipes located next to this.


I'm not sure how to perform the operations you requested with the boiler. The service panel contains several switches (no dials). The boiler itself is located utility room adjacent to the kitchen. (This room includes terminals for washers and dryers).


The repair did shorten the pipe I circled in my picture by 20mm, if this is a pressure valve, may this affect the system pressure?

Hello again,

Shortening the pipe would make no difference. Draining the boiler then not properly re pressurizing it would make a difference.

A competent boiler man on site could most likely have this sorted out in a few minutes. He would assess the boiler pressure first by lifting the lever on the boiler pressure relief valve, if water did not come out in a pretty heavy blast, he would open the water valve that directly feeds water into the boiler... that valve is within 5 or 10 feet of the boiler in most cases.

Once the boiler ;pressure was established at 15 to 25 pounds per square inch he would start the system, and if there was no water flow he would bleed air from the system at all of the air bleeds especially those for the lower floor and at the pump.

Odds are in the 95% range those measures would cure the problem... if not, he would consider that solder from the leak repair could have gotten into the motorized valve and is holding it closed (very very slight chance of that)

Tell me please if water squirts out of the air vents near the top of the radiators when you open them...tell me if water barely runs out, or squirts out with some force.

Chances are in the 95% range that air is trapped in the loop that stays cool... I would like to stay focused on that for a bit longer.