Central heating pump on the way out?

[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.

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[TD="colspan: 2"]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)
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Thanks for any replies.

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[oz-plumber]

Sounds more like the zone valve than the pump.

But on a technical note -

How would you and what method would you use to install an air bleed screw on the pump head?

 

[PlumbBobBob]

i agree sounds like a fault with the zone valves possibly wiring needs looking at. have there been any works carried out on the system lately?

 

[rcflyers]

i agree sounds like a fault with the zone valves possibly wiring needs looking at. have there been any works carried out on the system lately?

I replaced the hot water cylinder zone valve a few months ago.

 

[PlumbBobBob]

did you replace the wires like for like? it could be that a wire is not where it should be cutting out the heating when the water is being heated.

 

[rcflyers]

did you replace the wires like for like? it could be that a wire is not where it should be cutting out the heating when the water is being heated.

Yes, I took pictures and drew diagrams of the wiring before I touched it so I am confident it is as it was.

 

[rcflyers]

did you replace the wires like for like? it could be that a wire is not where it should be cutting out the heating when the water is being heated.

The heating has been off for a few hours.
I turned the hot water heating on, waited a few minutes for the pipes to the cylinder to heat up then turned the heating on and sure enough the heating zone valve opened and then warmed up within a few seconds so it would appear that both zone valves are open.
It seems that the water flow is favouring the cylinder over the radiators.

 

[Simon F]

the cylinder is an easy route.
is there not a valve to restrict flow to the water side?
with just the heating do the radiators work well?
just set the water to be on at a different time to heating


yes pumps do slow down, get tired.
what speed is is set to? see if putting it up a speed helps.

 

[rcflyers]

the cylinder is an easy route.
is there not a valve to restrict flow to the water side?
with just the heating do the radiators work well?
just set the water to be on at a different time to heating

That's what I thought, the water will go the route of least resistance, i.e through the cylinder.
When the cylinder zone valve closes the radiators all work perfectly.
Maybe I need a gate valve on the cylinder return pipe to restrict the flow somewhat?

 

[rcflyers]

the cylinder is an easy route.
is there not a valve to restrict flow to the water side?
with just the heating do the radiators work well?
just set the water to be on at a different time to heating


yes pumps do slow down, get tired.
what speed is is set to? see if putting it up a speed helps.

The pump is on it's maximum speed now.

 

[Jimbob]

Could be the flow through the cylinder needing to be balanced down. But it's unusual for all radiators to completely stop working. Its possible you have a knackered pump or maybe debris if your system

 

[rcflyers]

Could be the flow through the cylinder needing to be balanced down. But it's unusual for all radiators to completely stop working. Its possible you have a knackered pump or maybe debris if your system

I guess a gate valve on the cylinder flow or return will sort that out?

 

[Jimbob]

Yes that would stop all the flow going to the cylinder