Help with boiler cutting out to early and bypass valve

[marc1977]

Hi,

My boiler is cutting out before my rads are getting properly hot. Im 99% sure its the "water thermostat" doing its job and cutting out as the water temp gets up to max heat as the feed pipe is boiling hot but the return is only luke warm. It does restart itself once the water cools down and generally works perfectly fine.

For some reason the system seems to struggle to disperse the heat. The pump appears to be working fine and there is no air in the system. I also had the boiler serviced recently and it was apparently in good condition. Ive also turned the boiler temp up to maximum.

I was wondering if an incorrect setting on the bypass valve could cause an issue? Also can anyone help with what my setting should be? I have a grunfoss pump on speed 3 and Worcester camry greenstar boiler. Ive tried to look up the flow rates etc that you need but cant find them anywhere?

Any ideas and help much appreciated!

 

[Last Plumber]

Hi,

My boiler is cutting out before my rads are getting properly hot. Im 99% sure its the "water thermostat" doing its job and cutting out as the water temp gets up to max heat as the feed pipe is boiling hot but the return is only luke warm. It does restart itself once the water cools down and generally works perfectly fine.

For some reason the system seems to struggle to disperse the heat. The pump appears to be working fine and there is no air in the system. I also had the boiler serviced recently and it was apparently in good condition. Ive also turned the boiler temp up to maximum.

I was wondering if an incorrect setting on the bypass valve could cause an issue? Also can anyone help with what my setting should be? I have a grunfoss pump on speed 3 and Worcester camry greenstar boiler. Ive tried to look up the flow rates etc that you need but cant find them anywhere?

Any ideas and help much appreciated!

If the By-pass was passing too much then the return would be hot. That could knock the Boiler off but in your case the return is cool so it sounds like poor circulation.

 

[snowhead]

If the flow is hot and the return is cold then the pump can't be working fine.
It's not the bypass either as L-P has said.
If the flow and return at the boiler were hot and the return beyond the bypass was cold then it would be the bypass.

Open up the bypass fully and see if the return at the boiler heats up.

 

[marc1977]

Ahh yes, the return is only cool above the bypass, its hot below that on the return. However the bypass is already set to 0.5 which is nearly the max it can be set too? Its only 18 months old as its a new system so doubt its broken??

 

[Best]

Don't forget the bypass is there for a few purposes. Firstly it should ideally only open and bypass when nearly all circuits close down. (If it does open it derates the power of the pump).
It is also for keeping water flowing in boilers sometimes and to prevent system noise.
I would try shutting the bypass valve down, but this is usually best done by a heating engineer. Some system designs are wrong and can pump over.
If it still remains poor circulation, then it is the pump at fault.

 

[Best]

I assume the pump is correct type for system size?

 

[marc1977]

I think so but dont know how to check that? I had it converted from a 1 pipe to a 2 pipe 18 months ago and the plumber said the pump was was fine but that it should be on speed 3 as i have a big house. Also Im sure the boiler didn't cut out as often last winter.

 

[Best]

Pumps can start to drop in performance. The colder the weather becomes, the more noticeable the lack of heat.
First rule out the bypass valve by having it set correctly. If system still not working properly, then it must be the pump half working unless there is blockage in pump or pipes

 

[marc1977]

Thanks. Any advice on how i can set it correctly?

 

[Best]

Thanks. Any advice on how i can set it correctly?

Would be better your heating engineer do it, but a very rough guide would be to turn bypass fully off clockwise and run the heating just on rads with only one radiator turned on. Then after rad is hot, turn the bypass slightly on while holding your hand to the pipe. Slowly turn further until you have heat bypassing.

 

[Harvest Fields]

Not read all posts so sorry if I missed anything. Sounds like a circulation issue to me. The pump is probably spinning but not enough to get a good flow around the system.