>Can anyone shed any light on how much of a problem the above issues
> >are and how pumps are rated?
The Keston 130 quotes a minimum flow rate of 50l/m (0.83l/s as Grundfos
> quote it). If you download the product data for the pumps you mention (big
> pdfs I'm afraid) you'll see that the 15-60 just can't come close to shifting
> that much water but the 25-55 should be ok for heads of less than 2.5m.
Thanks - having read the manual again last night I was planning to look this up based on flow rate so you've saved me the effort. They dont make things easy do they?
Are hearing signs of low flow - localised boiling when the boiler is at full > power?
It's a noisy beast so i very much doubt i'd hear it above the fan. However, it does seem to short cycle which is likely to be related. The boiler has a pump over-run facility which can be wired out of circuit (and of course has been) so a minor rewire would probably solve the localised boiling i think i can hear when the boiler switches off.
In short, I think your man is right about the pump :-(
I'd come to the same conclusion (he was from Keston after all and wasnt interested in actually doing the work) but am wondering about the relative costs of getting the pump replaced now (when we've a lot of other expenses) versus shortening the life of the boiler slightly but not having that cost for some years.
> btw: On the bypass pipe being too small, unless it is microbore I doubt it,
> since the minute the loop goes on bypass, the boiler return temp will rise
> causing the boiler to throttle back meaning that the bypass loop never has
> to handle full power flow IMO. What size is this pipe?
the out and return pipes are 28mm (huge) for about a metre, then reduce down to, i think 22mm down under the floor into a loop of about
3m total length but a small section (maybe 20cm total ) of the loop near the pump is 15mm (again estimated). If we had the pump replaced that small section could go as well.
I'm assuming you
> have an automatic bypass valve in use.
You've lost me there - what would it look like and where would it be?. The system is plumbed in as S plan i think - seperate motorised valves on the DHW and CH, pump runs when either valve is open.
The Keston 130 is a commercial model which they pushed into the domestic market. I don't think it modulates. At 50 l/min minimum flow through the boiler that is commercial.
Yes, but not for long as we now have a wireless room stat that will live in the living room and the rads in there will not have trvs when we replace them in the next month or so.
I think you are saying that your pump overrun has been disabled and you are going to put it back? Def must have overrun & I think the only reason to disable it would be if it was handled by a separate (industrial type) controller.
I'm afraid I didn't read enough on the K130 and assumed it was a modulating type (variable output based on demand), as my own Keston Celsius 25 is, so my comments on throttling back and modulating do not apply. The effect of bypass coming into operation will be to raise the return temperature, which in itself will cause the boiler to switch off or will cause the outlet temperature to rise (after a delay) causing the boiler to switch off.
This does explain quite a lot, as you do say that the boiler runs in short cycles. The K130 has a huge 38kW output so you need a huge house to soak up that much juice. My Celsius 25 has a 23kW output and rarely runs at full power, it's minimum modulated output is 7kW and that's where it sits for most of the time. If you don't have a huge house or if the rads are shutting down with the TRVs, as the rooms approach demand temperature, then the massive boiler output will have nowhere to go & it will switch off not long after switching on.
You may wish to consider a boiler lockout which will inhibit the repeated short running. There are various on the market but I have not needed one and so cannot recommend. Some have been mentioned here so a google groups advanced search could help you.
An alternative to one large pump might be two of the type you currently have, operating in separate circuits, say one downstairs and one upstairs for example. I know that means pipe mods which you may not want to do.
28mm sounds ok for me, but perhaps this should have extended until the first split in the circuit rather than reducing to 22mm so soon.
It's one of these:
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, second item, differential bypass valve. It automatically passes water in the bypass loop when pressure rises above a preset value due to TRVs closing on the radiators. The fact that they automatically pass just enough water to compensate for each radiator as it closes makes them a must for any system IMO. The alternative is to use a simple gate valve as a bypass, which is a bit hit or miss as the setting is fixed and a compromise.
I notice you are also adding a wireless room stat. The living room isn't always the best place to place this, as although you are guaranteed a well controlled temperature in the room you use the most, you may have other heat sources in the room - decorative fire, lots of light, lots of people gassing ;-) - that may cause the heating demand to go off before the rest of the house is up to temperature. Best place is usually a heat neutral one so not the living room or kitchen and prob not a room that doesn't need much heat, say a bedroom. This usually points to the hall but as you have a wireless stat, you can always move it around and experiment.
Lastly as you appear to have a big house, I would consider separating it into a couple of zones with separate stats in each as it should control to temperature far better, but that's more work & expense :-/
This range of boiler is so simple it doesn't even have a pcb board. Keston were one of the first to have a top mounted downward firing burner spiral tube heat exchanger design. They are famous for short cycling, which Keston say does them no harm.
It needs to have the correct sized pump that will give the minimum flow through the boiler "at all times", the pipework upgraded and a by-pass installed and pump overrun facility re-activated.
To get the cycling down install a Honeywell CM 67 (or similar) programmers/stat. this has an anti short cycling function reducing the boiler on-off irritation. I would also fit a cylinder with a large quick recovery coil. A coil that can take all the boilers output. Better still install a direct acting heat bank or thermal store that will take all the boilers output and will not cycle when re-heating the water store. These boilers are good for this application.
Regarding installing two smaller pumps to supply two zones. This should be avoided as when one zone is off the smaller pump cannot guarantee the minimum flow through the boiler. Best have two large pumps if supplying two zones.
To be fair the manual does say it can be run as it is now but it can only be improved by rewiring. And it's free.
It's a big end of terrace house and even with the keston running it's been cold over winter - i'm not sure we got to the point where the thermostat cut in during the cold weather. A bigger pump might get the heat round better.
not that i can see.
I'd be happy to have one warm room! the stat was in the hall but the total volume of the hall is huge and it never gets warm. Wireless stat will let us play.
I'd thought of that as well but cant fund it right now - too much else to do. I'd rather spend the money on a nice gas fire and keep the living room warm even if the rest of the place is cold.
Ok. that's a lot of expense - i'm tempted just to let it break to be honest and then sort it out when it's replaced. At least that way i put off the expense for a few years. At the moment it's new kitchen, plastering, radiators etc etc.
Hi - there is one option thats cheap, if the figures add up in your case, and thats to add a 2nd cheap domestic pump.
When you run 2 pumps in series each pump sees half the back pressure, so to work out the flow you then get, you use one pumps data but with half the pipe length and half the head that your system in fact has. I dont know if Im being clear here, so an example:
Say you have a 3m head and 10m of pipe to push through. With 2 series pumps each pump will behave as if it has a 1.5m head and 5m of pipe - hence you get more flow.
Series plumbing pumps is not difficult. If this gets you where you need to go it could be a low cost option, plus has the advantage that if/when a pump fails the system will still function, the way it does today.
For a 2nd pump parallel you use the figures without halving them, and you get twice the rated flow with 2 similar pumps.
The problems is that if one fails it will not give the minimum flow through the boiler and the user may be unaware that a pump has failed and the boiler will be affected. The correct sized pump needs to be fitted.
This system needs the right pump and the pipes sorted ASAP. If not this boiler will expensively fail. They are good boilers and worth looking after.
To be honest the Keston engineer who visited didnt seem that worried about it according to my wife. He said it would shorten the life of the boiler but not that it would fail in the near future.
Not at all. However, it's likely to be an expensive fix and since we're currently without a kitchen and have ceilings down in 3 rooms there are other priorities right now. The previous owner had the boiler installed 3 years ago and the engineer (from Keston) said there was no damage to the boiler. Another year is unlikely to kill it but if we will get someone to price the work if it makes you feel better. Where should i source a 25-55 pump? Grundfos told me that the Discounted Heating price is above rrp and that small merchants are unlikely to be cheaper.
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