Centra heating pump does not run constantly when heating on

[dazjstuart]

Hi,

I hope this isn't a silly question but when the heating is switched on (or comes on on the timer) the pump starts circulating shortly followed by the boiler firing up. When it gets everything up to temperature the boiler switches off as one would expect but then the pump switches off too. Eventually they will both fire up again but by that time some of the radiators are sometimes starting to get cold. Surely this isn't normal, every other system I have seen the pump runs as long as there is something switched on and the boiler goes off and on as required?

If indeed this is not normal then what would cause it? Baxi solo gas boiler and Grundfos pump, cant remember the model, its red and has 3 selectable pump speeds on it.

Thanks

 

[muggles]

IIRC the Solo doesn't need a pump overrun so your setup is correct. If you're finding that temperatures are not constant, re-balancing the system and fitting a more accurate thermostat would help

 

[dazjstuart]

Thanks for that. TBH the radiators have been fine recently but the hot water tank (in the attic) never gets very hot off the heating and needs to be boosted by the immersion to give me properly hot water.

To describe my system further, I only have one "zone" the heating and hot water are on the same circuit and you cant have one without the other. All the radiators are on the same (first) floor with the boiler halfway up the stairs (first floor self contained flat). I previously had a problem with the system pumping over into the header tank in the attic and turned the pump down from 3 to 2, that solved that problem, but it seems to me now that the system isn't strong enough to pump water up to the hot water tank in the attic, it gets warm through convection but I don't think its really circulating through the hot water coil.

Maybe I'm overcomplicating it, but I can't see why the system would want to pump water up to the attic, it will just take the path of least resistance through the radiators and leave the loop going up the attic static, but then how to heating systems over several floored houses work?

 

[DP]

You have a plumbing issue not a boiler problem. Get that seen to as pump over should not occur.
Also, boiler controls the pump (if I remember correctly pump is wired to the boiler so boiler decides when pump should run), so when boiler has done its work, pump will also stop

 

[Agile]

You are overcomplicating the situation by trying to think ( wrongly ) about how it may work.

You don't explain how you suddenly seem to be in possession of a system with substandard ( or no ) controls.

It would be possible to fiddle with it to get better hot water.

But the proper solution would be to have the correct controls fitted. Depending on the layout that would probably cost about £300-£400.

Tony

 

[dazjstuart]

Suddenly in possession because I have just moved in!

If I shut off a few of the radiators then it improves. When I build up some funds I'll be replacing the whole lot with a combi system anyway so I'm just wondering if there's something obvious I can do to get a more operable system in the meantime. It doesn't pump over with the pump on 2. I presume by correct controls you mean fitting a motorised valve somewhere that can select between heating, hot water and both?

You are overcomplicating the situation by trying to think ( wrongly ) about how it may work.

You don't explain how you suddenly seem to be in possession of a system with substandard ( or no ) controls.

It would be possible to fiddle with it to get better hot water.

But the proper solution would be to have the correct controls fitted. Depending on the layout that would probably cost about £300-£400.

Tony

 

[Agile]

Yes, you need one or two motor valves and the associated thermostats to give a properly controlled system.

Although I have not seen your system my advice would probably to keep the existing arrangement rather than fitting an expensive combi.

The stored water is far better than a combi and I would say you would be going from a better system to a worse one.

To replace with a combi would be about £2200 and to fit the controls about £300-£400.

The Solo is a fairly basic boiler, pretty reliable although not terribly efficient by modern standards. Once you have the controls fitted then at any time you could replace the boiler alone for about £1400 although my advice would be to keep the Solo for the time being.

So controls and a new heat only boiler would be about £1800 and you would have a better system at a lower cost.

Tony

 

[dazjstuart]

Thanks for your advice. The boiler is about 4 years old apparently. Why do you say that stored hot water is better than hot water on demand? I know that a tank is pretty efficient at heating water whereas a combi is less so, but surely this would be offset by only heating the water you need?

There's a couple of other issues driving my thinking too, there is a lot of pipework between the tank and taps, takes about 30s to get hot water at the taps, and a possible loft conversion in future would mean getting rid of the stuff in the loft anyway.

If installing the controls you suggest would only be a few hundred pounds I'll probably do that later in the year when I redecorate the hallway, I believe the majority of the heating pipes are under the hallway floor.

 

[Agile]

If a Baxi Solo it will be over 10 years old if its really that model and non condensing.

Can you advise exactly what model you have?

Any boiler only 4 years old would need to control the pump and would have a minute or two of pump over run.

A tank and combi have about the same efficiency for normal family use.

The advantage of a tank is you can get a greater hot water flow. It can supply two outlets at the same time. A combi only one outlet. A tank also has a backup immersion heater too.

I don't see any advantage paying to replace a better system with a worse one.

Tony

 

[dazjstuart]

I'll have a look when I get home for a model number etc but its definitely a Baxi Solo, the previous owner advised it was replaced in 2011 and it does look fairly new. It is condensing, well I presume it is, it has a pipe that runs into the drain outside. It maybe does have a slight overrun, I've never sat and monitored it exactly I have only noticed them both not running then both starting up again.

Fair point about having an immersion as back up, always nice to have. My previous flat had a combi boiler and unless I'm very much mistaken you could open 2 hot taps, obviously with a reduction in flow but I can't see that ever being an issue, its a 2 bed flat with 1 bathroom, I could see it being an issue in a larger family home with multiple showers etc. You would get a more powerful shower off a combi aswell would you not?

 

[muggles]

If a Baxi Solo it will be over 10 years old if its really that model and non condensing.
Tony

The Baxi Solo is a current production model Tony, although it will be phased out this year

 

[Agile]

In that case it is a Solo HE which is a completely different boiler. Bit if a bodge design and not terribly reliable but they are condensing and quite modern. Not sensible to unnecessarily replace it when its so new.

But they should have the pump wired back to the boiler as they need the over run.

They are often installed wrongly and you should follow the pump wiring to see if it is correct or not.

A standard combi only gives about 8-9 litres per minute which is not enough to run two outlets very usefully.

All I can say is that I would always keep a stored water system.

Tony

 

[DP]

But they should have the pump wired back to the boiler as they need the over run.

NOT ALWAYS!
RTM
Reminds me of what you said about people who fail to read the manual

 

[gas112]

Jesus Agile getting so much wrong in one thread