CH Pump Performance (or failing)

[ChrisNason]

I'm struggling to keep both the heating and hot water system running. For some time the Lounge radiator has been slow to heat up. About 6 months ago I bit the bullet and got a plumber to investigate. He changed the pump (to a Grundfos 15/60 Super Selectric) and balanced the radiators. He had real problems getting it sorted and in the end most radiators were turned right down to just a crack open.
For most of the winter all was well but now I'm getting (mostly) cold radiators. I can fix it by turning off the Hot Water circuit which diverts the flow to the radiators (albeit slowly). Just once I've woken up to cold water and perfect radiators (my theory is that the first circuit to demand gets the flow)
The system also has a gate valve for bypass (2 Honeywell valves) which is screwed down almost closed to get the flow in to that lounge radiator.
The radiators all heat up together when working. I leave the hot water system on overnight to fully replenish.
Have I ruined the pump by having the gate valve screwed down to far or have I got blocked pipes?

 

[Eco-Squad]

Does sound as though your system is full of sludge. Check some of this out first though.
Shutting bypass completely will help get the heat to the rad in the lounge but you may have to open it a little if you dont want your boiler to start kettling.
Look for a setting on this valve where you can get best of both.
You didnt mention which boiler you had fitted!
Fitting a balancing valve close to the cylinder on the return will stop the coil from robbing your system of heat.

A less likely but nevertheless important point:-
A boiler which hasn't been serviced will be a lot less efficient as well as potentially dangerous. If it hasn't been done attend to it now!

 

[Agile]

There should be a lockshield valve on the heating circuit to balance the flow between CH and HW. Rarely fitted though!

Your problem might be caused because the valve is not closing the HW port when the cylinder is to to temp!!!

Tony

 

[ChrisNason]

Does sound as though your system is full of sludge. Check some of this out first though.
Shutting bypass completely will help get the heat to the rad in the lounge but you may have to open it a little if you dont want your boiler to start kettling.
Look for a setting on this valve where you can get best of both.
You didnt mention which boiler you had fitted!
Fitting a balancing valve close to the cylinder on the return will stop the coil from robbing your system of heat.

A less likely but nevertheless important point:-
A boiler which hasn't been serviced will be a lot less efficient as well as potentially dangerous. If it hasn't been done attend to it now!

The Boiler is a Potterton Kingfisher MF 40-100. It has recently been serviced (about 10 Months) and it is not on very often. The pipes from and to it are almost the same temperature (very hot).

There isn't an adjusting valve on the hot water circuit (just the Honeywell). I'm sitting here this morning with very cold radiators. I don't think it can be sludge as the plumber drained down the system when he fitted the pump (and put in a treatment).
I'm just thinking I might open all the radiators a crack (and be prepared for the loung going cold)

 

[bpowell555]

Did it ever work well - before the lounge rad started to die and before you swapped the pump? Sounds like the pump didn't do anything so it is a problem with the pipework?

 

[ChrisNason]

Did it ever work well - before the lounge rad started to die and before you swapped the pump? Sounds like the pump didn't do anything so it is a problem with the pipework?

Good point. maybe the lounge has always been that way. I had to replace the original because it had a pin hole leak from the top. It was bent around the bay window. The new is shorter but double.

The pipework is 3/4 inch for the first metre before splitting to 1/2 inch Tee for front and rear circuits. The rear circuit has 2 bedrooms and a dining room. The front circuit splits again with one side feeding hall and bathroom and the other side feeding Lounge and front bedroom.

Should the 3/4 inch be extended?

 

[ChrisNason]

Having now studied the pump action over an evening from cold (in the radiators) I can see that the flow is very slow. The pump is on it's fastest setting but it takes about 35 minutes for the cold return pipe to start to have any warmth (on each radiator). During this, the boiler is only coming on for about 2 minutes before turning off for about 4 minutes.
Is this normal?

 

[ChrisNason]

Can I run the the system with the bypass off? With it open about 1/2 a turn the flow nearly stops to the radiators.
I can't think what else I can do to improve things.

 

[ChrisNason]

Had another poke around today and spent most of the day emptying and cleaning the supply tank in the loft. I was thinking that any crud that got in to the system would cause a blockage and slow down the pump.

Having now fired up the system it's even worse. Now I have all the down stairs radiators stone cold but everything upstairs boiling (eventually).

Would this indicate that the hot water is rising and heating everything above the landing.

In which case has this pump failed after just 6 months?

 

[ChrisNason]

Now solved! See this post...

//www.diynot.com/forums/viewtopic.php?t=126303