pump or circulation problem

[NatB]

I've been having problems whereby the boiler heats the rads ok but after a time will shut down the heating, cool then fire back up again. The flow pipe is hot at this point but the return is nearly always cool.

I thought it may be that the system needs balancing which I have tried to do but found another (related?) problem in that not all the rads are getting hot.

I've opened up all the lockshieds and fired up the boiler. It seems the system is split between the rads upstairs (same floor as the boiler) and downstairs. The upstairs all get hot and toasty quickly whilst downstairs the first two small rads get hot then the rest only get warm at best and one doesn't get warm at all as the boiler eventually turns off (flow and return hot hot)

The boiler is a Baxi 105e with 3 biggish double rads, 1 single big and 5 small rads.

Pump failing or something more serious? I opened up the screw on the pump and got a little woosh and a steady trickle of water.

 

[stem]

I've been having problems whereby the boiler heats the rads ok but after a time will shut down the heating, cool then fire back up again.

Do you mean that the boiler goes off for a long time and the whole system cools? If not, are you referring to a cyclic on/off firing cycle once the system has warmed up. If so, that is the normal operation of the boiler thermostat, otherwise the water would get hotter and hotter and eventually boil.

The flow pipe is hot at this point but the return is nearly always cool.

Can you be a bit more specific here, the water in the return pipe will always be cooler than the flow because of the heat lost by the radiators, but it shouldn't be "cool" once the system has been operating for a while. Are you sure you have identified the return pipe correctly? Maybe there is insufficient flow of water around the system. Is the pump old or sludged up? What speed is the pump on? Do you have a manual by-pass valve that has been opened too much allowing the water to short circuit the radiators? (The return pipe would be hot then though).

I thought it may be that the system needs balancing which I have tried to do but found another (related?) problem in that not all the rads are getting hot

I've opened up all the lockshieds and fired up the boiler. It seems the system is split between the rads upstairs (same floor as the boiler) and downstairs. The upstairs all get hot and toasty quickly whilst downstairs the first two small rads get hot then the rest only get warm at best and one doesn't get warm at all.

It does sound like a balancing issue to me, as the majority of the water is taking the easy route around the upstairs radiators all on one level rather than taking the fall to downstairs and then the rise back up. This also goes against the natural flow of, hot water rising, cooler water falling. I would close all of the upstairs lockshield valves completely, then when the downstairs radiators are hot, just crack the upstairs lockshields open slightly. If a radiator gets hot at this point leave it at this setting, Then open the ones that aren't hot a little more until they are. The goal would be to keep the upstairs radiator lockshields as closed as possible to give satisfactory operation of the upstairs radiators yet to allow the force of the pump to feed the downstairs radiators. Expect the valves on the larger radiators to be open more to achieve this. You can then repeat the excercise downstairs if required. This should improve matters in the short term. How to balance radiators properly can be found by clicking here

the boiler eventually turns off (flow and return hot hot).

That's normal. Once circulation stops any water pipe connected to the boiler will get hot by conduction from the residual heat.

 

[NatB]

I've been having problems whereby the boiler heats the rads ok but after a time will shut down the heating, cool then fire back up again.

Do you mean that the boiler goes off for a long time and the whole system cools? If not, are you referring to a cyclic on/off firing cycle once the system has warmed up. If so, that is the normal operation of the boiler thermostat, otherwise the water would get hotter and hotter and eventually boil.

The flow pipe is hot at this point but the return is nearly always cool.

Can you be a bit more specific here, the water in the return pipe will always be cooler than the flow because of the heat lost by the radiators, but it shouldn't be "cool" once the system has been operating for a while. Are you sure you have identified the return pipe correctly? Maybe there is insufficient flow of water around the system. Is the pump old or sludged up? What speed is the pump on? Do you have a manual by-pass valve that has been opened too much allowing the water to short circuit the radiators? (The return pipe would be hot then though).

The original problem was the system would cool all the way down to lukewarm before the boiler fired back up again, during this the return pipe (at the boiler) would never get above warm.

The two main rads downstairs were taken off the wall and cleaned a while back and a magnaclean installed afterwards so while it may be sludgy it shouldn't be that bad plus when the rads do get hot they get hot pretty much all over.

I have checked the pump but I don't see how I can change the speed (grundfos up 15-60 p/n 59926502) as no selector switch on the side.

I thought it may be that the system needs balancing which I have tried to do but found another (related?) problem in that not all the rads are getting hot

I've opened up all the lockshieds and fired up the boiler. It seems the system is split between the rads upstairs (same floor as the boiler) and downstairs. The upstairs all get hot and toasty quickly whilst downstairs the first two small rads get hot then the rest only get warm at best and one doesn't get warm at all.

It does sound like a balancing issue to me, as the majority of the water is taking the easy route around the upstairs radiators all on one level rather than taking the fall to downstairs and then the rise back up. This also goes against the natural flow of, hot water rising, cooler water falling. I would close all of the upstairs lockshield valves completely, then when the downstairs radiators are hot, just crack the upstairs lockshields open slightly. If a radiator gets hot at this point leave it at this setting, Then open the ones that aren't hot a little more until they are. The goal would be to keep the upstairs radiator lockshields as closed as possible to give satisfactory operation of the upstairs radiators yet to allow the force of the pump to feed the downstairs radiators. Expect the valves on the larger radiators to be open more to achieve this. You can then repeat the excercise downstairs if required. This should improve matters in the short term. How to balance radiators properly can be found by clicking here

the boiler eventually turns off (flow and return hot hot).

That's normal. Once circulation stops any water pipe connected to the boiler will get hot by conduction from the residual heat.

I have a digital thermometer so I'm going to try and rebalance with that but the downstairs rads aren't gettin hot and one not at all when everything is fully open.

While everything is fully open the boiler does, at least, seem to fire, heat, off, fire, heat a lot better. The temp neons in this situation don't hit 0 and the return pipe is hot to the touch.

Thanks for the reply.

 

[stem]

Sounds like you have covered most bases. The only bit that puzzles me is why the boiler cools down to lukewarm, unless a room thermostat is overriding it

I would have a go at trying to get the downstairs rads working to some extent manually first, otherwise it will take you forever, if you were to start with all the valves fully open (or closed) and make significant adjustments to the others, that will change the pumps pressure on those already set, meaning they will have to be readjusted, so you will have to start all over again. Once you get all of the rads heating up, then use the thermometer for final tweaking. If you have TRV's make sure they are fully open whilst balancing.

From memory, I think I started out with:
Small upstairs radiators open quarter of a turn.
Larger upstairs radiators open between quarter & half a turn.

Small downstairs radiators open 1 turn.
Large downstairs radiators open 2 turns.

This is very rough but it might help to get you started. You can refine it a bit further if you like, by closing those nearest the pump slightly more and opening those further away slightly more.

 

[NatB]

That was the puzzle that got me to attempting to balance the system to try and at least rule that out.

I've now taken out the burners and giving it and the fan assembly a good clean to see if that helps.

Still stumped on changing the pump speed on a Baxi 105e. No switch even though the online manual indicates there is nor can I find that actual part number on sale.

Thanks.

 

[stem]

A standard Grundfos UPS 15/60 has a 3 position rotary switch on the face of the terminal box.

Pump

• stem
• 7 Jan 2010
• 2

I thought that the Baxi version was basically the same motor and head, but with special mounting and air vent on the top.

Although if the system used to work OK and the speed of the pump hasn't been changed I wouldn't have thought it would be the setting that's wrong. I seem to remember too that some baxi's have a pump failure lamp that illuminates if the pressure is too low.

I wouldn't expect the burner to be a problem as you say it is capable of getting the boiler hot when it is lit. Sounds to me like it's more likely to be a control issue.

 

[NatB]

Thanks.

Can't find the part number online from the pump currently installed but both boilers (two baxi 105e's) have the same pump head without a speed selector. An engineer changed one of them last year and that doesn't have a speed selector so unless they've changed it recently I don't know what pump head to use should I need a new one nor how to change it.

The new baxi 105e manual indicates the speed selector but not on my boiler.

The balancing has helped a lot so the rads are staying hot during the cycle. The boiler now kicks back in when the flow temp drops to 40 or 50 so the rads are just being kept hot now which is what I expect.

Very difficult to balance though as a combination of 22mm flow, 15mm branches and 8mm to some of the rads doesn't give me even flow temps. Ended up doing it by hand rather than the thermostat.

Now, I haven't got any rads with the lockshield fully open..is this normal or is it more efficient that the last rad are fully open?

 

[stem]

The pump will be able to provide a certain maximum flow & pressure. You have to distribute that around nine radiators, if one valve is fully open, you may find that as a lot of water flows through that one, there may not be enough for all of the other 8 and a couple cool.

You could always try opening up the furthest one fully and see what happens to the others.

It won't effect the operating efficiency of the boiler as it will just put the heat back into the water that the radiators have lost to the rooms.

both boilers (two baxi 105e's) have the same pump head without a speed selector.

You have two boilers? are they connected?

An engineer changed one of them last year and that doesn't have a speed selector

Some of the newer higher efficiency rated pumps have an automatic speed selection that slows as the demand falls. maybe you have one of those.

 

[NatB]

I've opened up the last lockshield and whilst it's still cycling it's not as bad.

I've come to the conclusion that the pump needs looking at as I can't even get the flow temp at the first rad to match what the boiler is pushing out.

I think this then causes the boiler to modulate as the drop across flow and return is just to high, manual indicates 11c is desired but I can't get that across any rads.

I'll make a separate post in regards to which pump I should be looking at as I definitely don't have a speed switch and the manual indicates I should have.

Cheers for the help.