Bypass question

[MickyP10]

Hi

Radiators are significantly hotter on max pump speed, so I thought it might be underpumped. Then I spotted a manual bypass, originally set one turn out from fully in. If I reduce this to, say, a quarter of a turn out, flow improves, radiators are warmer and boiler thermostat can be reduced.

At least two radiators are non TRV. Could the bypass be shut off completely and, maybe, pump speed set to next slowest setting?

 

[stem]

Depends on your type of system. "S" or "Y" plan, combi or not and whether your boiler has a pump overrun or not.

It could be possible if you have 2 port motorised valve that when your room stat switches off and closes the valve there's nowhere for the water to go and your boiler overheat will trip. Also in the summer when you are using hot water only and the radiator circuit is off, there's no where for the water to go.

If the system is designed with a bypass then it's been put there for a reason. You could consider changing the manual valve for an automatic one which only opens when there is no demand at the radiators. Manual bypass valve are generally seen as being inefficient as water will be passing through it when the radiators need it, and many people turn up the pump to compensate using more electricity

 

[MickyP10]

Depends on your type of system. "S" or "Y" plan, combi or not and whether your boiler has a pump overrun or not.

It could be possible if you have 2 port motorised valve that when your room stat switches off and closes the valve there's nowhere for the water to go and your boiler overheat will trip. Also in the summer when you are using hot water only and the radiator circuit is off, there's no where for the water to go.

If the system is designed with a bypass then it's been put there for a reason. You could consider changing the manual valve for an automatic one which only opens when there is no demand at the radiators. Manual bypass valve are generally seen as being inefficient as water will be passing through it when the radiators need it, and many people turn up the pump to compensate using more electricity

Thank you. The system was fitted badly, so I'm not assuming the plumber had a good reason for fitting the bypass (ie no drain, no thermostat, no commisioning details, etc). I see your point and will do some more tests.

BUT would a variable pump detect when to back off the flow and compensate automatically? I'm thinking of a Grundfos Alpha here.

Thanks again for your help

 

[ChrisR]

Bypass would be to cool the boiler, not to give the pump an easy life!
WHAT BOILER IS IT?!!
WHAT VALVES ARE THERE?!!

 

[MickyP10]

Bypass would be to cool the boiler, not to give the pump an easy life!
WHAT BOILER IS IT?!!
WHAT VALVES ARE THERE?!!

Firebird s90.

There are two valves, but I'm not at home so can't give any info yet. Just thinking out loud, that's all. If the bypass is turned in more, the radiators run hotter and I can turn the boiler thermostat down. Or I can open the valve up, wick up the boiler stat and get cooler rads. Seemed a bit pointless.

 

[Nixt]

Firebird is an oil boiler and if so it's control stat should be set to full (80) winter (CH/HW) or 60 deg summer (HW only). Your house temp should be controlled by a r/stat. If control stat too low, return temp drops and can cause cold water corrosion is combustion chamber.

 

[kevplumb]

Firebird is an oil boiler

theese right lad

return temp drops and can cause cold water corrosion is combustion chamber.

therefore it becomes a condenser

so allegedley more efficient if you belive that pratt prescott

 

[MickyP10]

Firebird is an oil boiler and if so it's control stat should be set to full (80) winter (CH/HW) or 60 deg summer (HW only). Your house temp should be controlled by a r/stat. If control stat too low, return temp drops and can cause cold water corrosion is combustion chamber.

Ah, thanks. But if I set it to 80, the boiler thermal protection cuts in due to residual heat build up. The pump stops when the boiler turns off, so the heat does build up. NB A pipe stat was fitted to fire the pump up when the boiler temp was getting too hot, but it wasn't successful. This was Firebird's suggestion.

I know the system has flaws. I figured the option was turning the bypass in and boiler temp down; turning the boiler temp up, opening the bypass and fully opening the non-TRV'd radiators to keep the heat out of the boiler or fitting an automatic bypass. Sounds like the first option! It just seems an uneconomical way of doing things.

The ONLY reason I started looking at the bypass situation was the fact that the rads run much hotter with the pump set to max, which is why I originally thought the pump was underachieving. I've tried to find out from Grundfos whether their pound-for-pound Alpha range of pumps flows more or less than the UPS 15-60 130 currently fitted. They're not helpful. If it flowed more, I'd have no qualms about sticking a new pump in, as I think it'll run things hotter and the bypass issue will subside; if it flows less, it'd be a waste of time.

Thanks for your answers, incidentally.

 

[Bigburn]

Mickyp10 wrote

The pump stops when the boiler turns off,

Then its wired wrong.

 

[MickyP10]

Mickyp10 wrote

The pump stops when the boiler turns off,

Then its wired wrong.

Agreed, but in my Firebird bumf the recommendation is for a pipe stat in certain circumstances; ie it's not std (although probably is now. This one's four-and-a-bit years old.) I've had two sparkies try and wire the pipe stat to the programmer and both failed. But this would be the answer to the problem.

 

[Bigburn]

You dont need a pipe stat.
What you need is a room stat.

 

[MickyP10]

You dont need a pipe stat.
What you need is a room stat.

Sparky no. three put a thermostat on the wall, which just turns the pump and boiler off simultaneously; sparkies one and two tried to wire the pipe stat to the programmer, but failed. Is a room stat summat else?

Edit to say sparky three couldn't get the pump to remain on after the boiler had switched off.

 

[kevplumb]

Edit to say sparky three couldn't get the pump to remain on after the boiler had switched off.

 

[MickyP10]

So you can see why I'm cynical...

 

[MickyP10]

And skint