2 condensing boilers

[ajrobb]

We live in a large 1930s chalet bungalow and our gas consumption is equivalent to 50,000 kWh/annum (was 63,000 before double glazing). When we moved in 7 years ago, we had the heating upgraded and that included two Keston Celcius 25 boilers (25kW condensing system boilers).

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• ajrobb
• 9 Sep 2010
• 2

Each of the boilers has its own circulating pump but the installers put these on a short circuit "to ensure adequate flow through the boilers" and fitted a third circulating pump to the cylinder and radiators. I have the hall radiator and one radiator in the lounge controlled by the room thermostat (valves always fully open) and TRVs on all the other radiators. I have a Flowmaster Titan 300 litre unvented hot water cylinder.

I have recently read that condensing boilers are more efficient if the mean temperature is kept to a minimum. My concern is that the current arrangement will have high (non-condensing) inlet temperatures.

With the three circulating pumps, I'm wondering how far I can safely close the gate valve on the short circuit?

 

[ChrisR]

[code:1]how far I can safely close the gate valve on the short circuit?[/code:1]


That should be an automatic bypass valve. (see the boiler instructions, which I believe will specify one, even if the Building Regs didn't) YOu'd just set the pressure for sufficient flow through the boiler(s)

I hope there's non return valves in there somewhere, otherwise when one boiler's off...

50k kWhpa seems a hell of a lot, that's 137 per day

 

[D_Hailsham]

We live in a large 1930s chalet bungalow and our gas consumption is equivalent to 50,000 kWh/annum (was 63,000 before double glazing).

Apart from double glazing, have you done any other insulation, e.g loft and cavity wall (if possible)? Loft should be 10-12 inches. There are very good deals available for low cost or free insulation. Check out Energy Savings Trust Grant Search

When we moved in 7 years ago, we had the heating upgraded and that included two Keston Celcius 25 boilers (25kW condensing system boilers).

That's a huge heat output, even for a bungalow. It would be worth checking what you should have by using the Boiler Size Calculator

I have recently read that condensing boilers are more efficient if the mean temperature is kept to a minimum.

Condensing boilers are more efficient when they are condensing. To do this the return (inlet) temperature has to be below 55C. The system, however has to be designed for this temperature as the output of the radiators will be affected.

My concern is that the current arrangement will have high (non-condensing) inlet temperatures. With the three circulating pumps, I'm wondering how far I can safely close the gate valve on the short circuit?

The temperature differential is determined by the pump speed (high speed = small differential and vice versa). According to the Installation Manual: "The optimum pump speed is also detected and automatically selected by the boiler".

I would leave the gate valve alone for the moment.

Personally I would be more concerned why I needed 50kW to heat the property.

 

[ajrobb]

Personally I would be more concerned why I needed 50kW to heat the property.

Cavity wall insulators say cavities are already full.

Loft insulators topped up what they could reach - not much.

I think 80m² of inaccessible voids plus skeilings etc has something to do with it. When I can afford to replace the 120m² roof...

 

[Paul Barker]

You must have loads of used ht leeds and electrodes littering the place. Have you had new exhaust flexible hoses fitted? Essential to do that. Have your thermal fuses popped yet? How is the gasket at the top of the heat exchanger?

I like an easy life, if I bought your bungalo I would rip those out and fit a worcester RI or Avanta or Alpha CDR. I would only need one, and fix it on the very rare occasion it were necessary.

your pair would keep me lying awake at night worrying.

I know, the installer told you they were the bees knees.

 

[D_Hailsham]

When I can afford to replace the 120m² roof...

If we assuming that your chalet bungalow is a two storey detached house, 10m x 12m, with cavity wall insulation, DG plastic windows and minimal loft insulation, the heat loss, using the calculator I pointed you to, is only 22kW!

 

[Onetap]

With the three circulating pumps, I'm wondering how far I can safely close the gate valve on the short circuit?

Did you employ Drivel/Water Systems?

It's a primary/secondary circulation system; leave the valve alone.

ISTR that Keston do some publications on linking their boilers, have a look at those to see if it explains it. I haven't studied this and do not claim that I have understood how it is meant to work. From the comments above, it looks like the system could operate adequately with one boiler.

The recirculated water (if the primary flow is greater than the secondary) will heat the return and reduce the boilers' efficiency.

 

[ajrobb]

It's a primary/secondary circulation system; leave the valve alone.

The guy that set it up was good and I don't want to say anything bad against his memory.

The recirculated water (if the primary flow is greater than the secondary) will heat the return and reduce the boilers' efficiency.

That is what I was worried about.

 

[petit_pablo]

we had the heating upgraded and that included two Keston Celcius 25 boilers (25kW condensing system boilers).

Funniest thing ive read in ages.

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• ajrobb
• 9 Sep 2010
• 2

This is what a gas mans nightmares look like

 

[PEDANTICVINDICTIVEMAN]

50Kw for a bungalow, whats it got Japanese paper walls with a tin roof..........

 

[ajrobb]

You must have loads of used ht leeds and electrodes littering the place. Have you had new exhaust flexible hoses fitted? Essential to do that. Have your thermal fuses popped yet? How is the gasket at the top of the heat exchanger?[

I'm pretty sure the exhaust hoses have been replaced. Lost count of circuit boards. Heat exchangers cracked etc etc.

When we moved in, there was a single 25kW boiler and coal effect gas fire. With original Crittall windows - freezing.

 

[mickyg]

is it just me or does that look like 22mm pipework all over ?

 

[Paul Barker]

Yes that is 22mm.

the only benefit of the two boilers is reliability, but that benefit is wasted in this instance because you not only have one well known unreliable band A boilers but you have a pair of the same, so have doubled your troubles.

If you have a crib so large that you need the equivalent of 50 1kw bars of a fire burning bright all round the house, then you have sufficient money to get those off the wall and replace them with a pair of ~15kw qaulity boilers or a single ~30kw boiler.

Otherwise you will continue to suffer interruptions through breakdowns.

I only own 4 boilers. If any one of them was one of those I would scrap it in the same day and put in one which is less flawed. That is not because I cannot fix it, it is because I don't believe in making work for myself.

the 4 boilers I own right now are an Avanta combi, a Vokera compact combi, a Potterton band A combi and a new Biasi combi in the flat I just finished renovating. So I am quite eclectic in mix, but all are boilers I have experienced very few problems with in my field experience. the reason for the variety is to do with what was available at the time. the Potterton was a couple of years old broken on ebay £170, fixed it with nothing more than knowledge, the Vokera was scrapped by a colleague, I fixed it with a second hand motorised head off a Biasi, a new fuse for the pcb and a gland seal. the Avanta i bought new, and the Biasi I bought new just lately because I was very short of remaining overdraft facility which is now up to the hilt. A singhle biasi would cost you less than the last 2 years breakdowns and probably work trouble free for 10 years. Just put a tap in the boiler room so the hot water side can be connected to something.

 

[ajrobb]

If you have a crib so large that you need the equivalent of 50 1kw bars of a fire burning bright all round the house, then you have sufficient money to get those off the wall and replace them with a pair of ~15kw qaulity boilers or a single ~30kw boiler.

Not having been in paid employment for over 2 years, I'm not in a position to splash the cash right now. Up until recently we had a reasonable maintenance contract with the installers, so the unreliability was more of an inconvenience rather than a cost. I think a single system boiler (30-40 kW) with weather compensation is the way to go. I may have to wait a little while for another breakdown to justify it.

 

[Lochy]

It's a primary/secondary circulation system; leave the valve alone.

Looks more like a simple Lead/Lag set-up to me. What ever it is, it's over-kill.