Poor heating after changing radiator (Ed.)

[Carly900]

Hi, new here so I’m hoping I’ve posted this in the correct forum. Would really appreciate some help with a central heating issue. We’ve had 3 plumbers out and no one has been able to diagnose or fix the problem. Hoping some experts here might be able to help!

The issue - over the last 4 weeks our hot water isn’t heating sufficiently / consistently. Some days we have plenty of hot water other days we only have time for a 5 minute shower before the water goes lukewarm and then cold. Our upstairs radiators are also not heating consistently. Some get hot others lukewarm, others barely heating at all. Was all working fine until recently.

The system - gas system boiler, underfloor heating on ground floor, normal radiators on first and second floors. Underfloor heating is controlled by individual thermostats in every room downstairs. Hot water tank is under the stairs and has a thermostat fitted, along with a recirculation system. The timing for the upstairs heating and the hot water is controlled by an electronic timer. The house was only built 2 years ago so everything is quite new. I have attached pictures of the plumbing around the hot water tank and the manifolds for the underfloor heating.

Relevant info - husband changed a radiator a few days before we started experiencing these issues. I’m inclined to think this is related but don’t rule out a coincidence!

Things we’ve tried so far (on plumbers advice) - opening the red valve that is on the top of the pipe that runs between the hot water tank and the underfloor heating manifolds. All that happened was the underfloor heating became less effective, so I think it just took away some of the flow to the underfloor heating. Having the valve half open seems to be the correct balance and is how it was when the system was working, so we’ve put that back as it was. Took off the thermostat on the hot water tank to see if that was the issue. Still experienced issues with hot water so have put that back on. Boiler seems to be working fine. No error messages and temperature increases/ boiler fires when we turn the heating / hot water on. Checked diverter valve - it seems to operate as it should when hot water turned on.

The hot water seems to work better if we just boost it rather than having it heating at the same time the central heating is on. But this was never an issue before.

I hope that gives enough info. I am at the end of my tether not knowing whether we will be able to have hot showers before work in the morning. If anyone has any suggestions please please let me know!

 

[Alec_t]

Circulation pump not fully functional?
Air in pipework?
Welcome to DIYnot!

 

[Stuckinarut]

Could be above, but you have an unvented cylinder, which ought to be worked on by a G3 registered engineer

 

[Carly900]

Circulation pump not fully functional?
Air in pipework?
Welcome to DIYnot!

Thanks! Is there an easy way for us to test whether the circulation pump is working? Would the circulation pump stop the hot water from working as well? How might we get rid of air in the pipework? We’ve already bled the radiators… anything else we should be trying?

 

[Alec_t]

Is there an easy way for us to test whether the circulation pump is working?

If it's running you should be able to feel/hear slight vibration of the pump. Check on each speed setting. If the speed settings produce no noticeable difference then I'd suspect a faulty pump motor winding.
Setting the pump to maximum speed would likely help with clearing any air-lock.

 

[Harry Bloomfield]

Assuming an airlock - You could also try, turning all but one radiators off, but one, then swap the radiator which is on, after a few minutes running, to a different one. Work your way round all of the radiators, and parts of your system. That should force any air, to collect at the radiators, and it can then be bled in the usual way.

 

[Carly900]

Assuming an airlock - You could also try, turning all but one radiators off, but one, then swap the radiator which is on, after a few minutes running, to a different one. Work your way round all of the radiators, and parts of your system. That should force any air, to collect at the radiators, and it can then be bled in the usual way.

Ok, thanks have just tried this. Individually each radiator heats up fine when all the others are turned off. We bled the radiators, turned them all back on and the radiators on the top floor seem fine, radiators in middle floor are warmish but not roasting… any ideas?

 

[Carly900]

If it's running you should be able to feel/hear slight vibration of the pump. Check on each speed setting. If the speed settings produce no noticeable difference then I'd suspect a faulty pump motor winding.
Setting the pump to maximum speed would likely help with clearing any air-lock.

The recirculation pump seems to be working ok… not sure how to change the speed though. There’s a little pin timer attached to it but not sure where the speed setting is.

 

[Alec_t]

not sure where the speed setting is.

It may not have one.

 

[Harry Bloomfield]

Ok, thanks have just tried this. Individually each radiator heats up fine when all the others are turned off. We bled the radiators, turned them all back on and the radiators on the top floor seem fine, radiators in middle floor are warmish but not roasting… any ideas?

Then, they need to be balanced..

 

[Carly900]

Then, they need to be balanced..

Sorry, this is driving us mad now. Balanced the system last night. When the heating was on on its own for balancing, all seemed to be working fine. This morning, hot water and heating on at the same time - some radiators lukewarm and water isn’t very hot. It’s almost like the system can’t cope with heating hot water and the radiators at the same time. But previous to this issue we were able to heat hot water and radiators together with no issues. Is there anything you can suggest?

 

[Harry Bloomfield]

Sorry, this is driving us mad now. Balanced the system last night. When the heating was on on its own for balancing, all seemed to be working fine. This morning, hot water and heating on at the same time - some radiators lukewarm and water isn’t very hot. It’s almost like the system can’t cope with heating hot water and the radiators at the same time. But previous to this issue we were able to heat hot water and radiators together with no issues. Is there anything you can suggest?

Some system don't allow heating to both, at the same time - are you sure it's not one of those?

That looks like it might be quite a complex system to attempt to balance anyway, are you sure the balancing has been done properly. If you have closed those valves down too much, then it will work, while ever there is no HW demand, but when there is HW demand, the HW circuit might be a much less restricted path for the circulation from the boiler, so that is the route it takes.

 

[Carly900]

Some system don't allow heating to both, at the same time - are you sure it's not one of those?

That looks like it might be quite a complex system to attempt to balance anyway, are you sure the balancing has been done properly. If you have closed those valves down too much, then it will work, while ever there is no HW demand, but when there is HW demand, the HW circuit might be a much less restricted path for the circulation from the boiler, so that is the route it takes.

Thanks so much. The system definitely does allow us to heat water and have heating on at the same time as we’ve had it running that way for 2 years and never had a problem. Always had loads of hot water and radiators all heated up with no issues.

It’s possible we haven’t balanced the system right as that’s the first time we’ve ever tried but we achieved a 12 degree differential for each radiator… just weird that now when we try to get hot water at the same time it’s not working properly. The mystery continues!

 

[Harry Bloomfield]

It’s possible we haven’t balanced the system right as that’s the first time we’ve ever tried but we achieved a 12 degree differential for each radiator… just weird that now when we try to get hot water at the same time it’s not working properly. The mystery continues!

Those symptoms - much less flow, when there is demand for water heating, suggesting you have restricted the flow to the heating system, too much. Water will obviously take the easiest route, and if that route is via the hot water cylinder coils....

 

[Carly900]

Those symptoms - much less flow, when there is demand for water heating, suggesting you have restricted the flow to the heating system, too much. Water will obviously take the easiest route, and if that route is via the hot water cylinder coils....

Would that not mean we would have really hot water and the radiators would be cooler? Whereas we have problems with both heating and hot water. Trying to riddle this through and feeling a bit stumped at the moment. Really appreciate your ongoing input!