Problem with radiators cooling down when hot water heating

[rcflyers]

I have a standard boiler that heats the hot water tank and radiators.
I have a timer which turns the radiator zone valve on at 6.00am then also turns on the hot water tank zone valve at 6.30am.

Recently I have noticed that when the hot water tank zone valve opens to heat the hot water tank, the radiators cool down to a point where they are almost cold.
When the hot water zone valve closes the radiators start to heat up again.

I realise that the hot water circulating from the boiler will take the path of least resistance but should I put some sort of valve on on the water tank circuit to restrict the flow so that all the hot water doesn't go through there?

Thanks for any replies.

 

[45yearsagasman]

A better description of your system with pics would help, but the simplest remedy is to fit a gate valve on the cylinder return pipe and adjust as required.

 

[rcflyers]

A better description of your system with pics would help, but the simplest remedy is to fit a gate valve on the cylinder return pipe and adjust as required.

Thanks, is there a difference in fitting the gate valve on the cylinder flow or return pipes?

 

[45yearsagasman]

Not really. Its traditional to fit on return. If you don't have enough room then the flow is next best. Has this fault just happened or always been there?

 

[rcflyers]

Ok, thanks.

It may have been there before but it has only been noticed in the last couple of months.

 

[Terry lambert]

I'm going to go out on a limb here and suggest you time your hot water to come on 30mins before your heating.

That way your cylinder will be satisfied, then giving full heat to your heating.

When your boiler is just topping up your cylinder you shouldn't notice the slight drop in temp to your rads.

If it's a new problem and worked fine before, maybe a tired pump ?

 

[rcflyers]

Our pump is a Grundfos UPS15-50.

Do they get tired?

If I put my ear close to the pump I can hear a soft crackling/popping noise which sounds like air in it.

I am struggling to see how there could be air in there.

There does not seem to be an air bleed screw on the pump head (although I could fit one)

See picture of pump and plumbing.

View media item 90493

 

[Terry lambert]

The silver disc on the front of the pump is the vent screw.

your air seperator could have carp in there, what's the general condition of the water?

Yes pumps do become tired. Some people might remove the vent plug and see if they can easily stop the pump turning with a flat blade screwdriver.

Or take the pump head off and see if you can easily stop the impeller turning with your finger, finger test

 

[rcflyers]

The silver disc on the front of the pump is the vent screw.

your air seperator could have carp in there, what's the general condition of the water?

Yes pumps do become tired. Some people might remove the vent plug and see if they can easily stop the pump turning with a flat blade screwdriver.

Or take the pump head off and see if you can easily stop the impeller turning with your finger, finger test

Thanks, Should pump be rotated so the silver disc is facing up in the air so any trapped air can be bled out?

 

[rcflyers]

I undid the bleed screw, some dark coloured water came out then all it did was drip some clear water. I let it bleed for 2 minutes and refitted the bleed screw.

The sound of air is still there inside the pump.

I could see the shaft spinning around ok but couldn't stop it spinning with a screwdriver.