Is my boiler undersized and what type is it?

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i live in a 5 bedroom detached house built in the mid 2000s that has recently been extended and now the radiators seem to take ages to heat up. An extra 3 large radiators has been added but I want to know if the boiler is sized appropriately for the house. There’s now a total of 22 radiators and the boiler is a Potterton Suprima 80L which is rated to 24kw. Water comes from a sealed unvented pressurised cylinder (megaflo) which is heated by the boiler.

So roughly speaking, is the boiler output appropriate?

Also, I’m trying to determine which boiler type/setup I have if I was to replace it. I don’t think the boiler has a pump as there’s a grundfos pump sited next to the water cylinder with a three way diverter valve.

Is this a ‘heat only’ type boiler? I originally thought it was a ‘system’ boiler as these are typical for unvented water cylinders but they also come with integral pump whereas mines is located separately.
 
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Is the house getting comfortably warm in all rooms? If it is, then the boiler is not undersized. If you want something more accurate, use the whole house calculation method to determine what size boiler is recommended.

Yes, you have a heat-only boiler, on a Y-plan system. Hopefully there is also a 2-port zone valve on your cylinder flow. If there isn't, there should be, as it is an essential safety device required by the regulations
 
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The house does get warm eventually but takes a while. Most of the radiators dont get upto to temperature until 2-3hours after the boiler fires and then another 1-2hours for the room to heat up. My timer in the morning is now set to start the boiler at 3.30am so at least the house is to reasonable temperature when everyone is up.

The Grundfos pump is a UPS 15-50 which is currently set to the highest speed and is rated to 5m head. I'm wondering if the pump is struggling and I should get a higher rated one.
 
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If the rads are taking that long to warm up there must be a circulation issue. It could be there's a bypass that's letting all the water round. 24kw should be plenty for a modernism house unless you're trying to heat a conservatory or something silly.
I'm sure the pros will be asking soon but until then If you close most of the radiators off does the remaining one heat up quickly? Can you find a bypass valve perhaps in the airing cupboard and does that part of the pipe heat up quickly?
 
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Hopefully there is also a 2-port zone valve on your cylinder flow. If there isn't, there should be, as it is an essential safety device required by the regulations

How would this 2-port zone valve be controlled ? What other components would be essential to safety ?
 
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Does the boiler have a heat setting on it? Is it set to maximum output?
 
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Yeah, it has a temp dial on the boiler which is turned up pretty much to the max end.
 
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I've come across these symptoms a couple of times before as a result of a by-pass valve as @John D v2.0 mentioned earlier.

The by-pass had been opened up too much and the water was circulating around that and going straight back to the boiler instead of the radiators. The clue was that whilst the radiators were still cool, instead of running flat out, the boiler wasn't firing much at all because a large percentage of the the hot water from its outlet was going straight back into the inlet.

Ironically, in one instance the owner had actually opened up the by-pass himself in an attempt to improve the circulation without realising what it actually did.
 
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How would this 2-port zone valve be controlled ? What other components would be essential to safety ?
It is wired through the over heat thermostat on the cylinder and closes if the boiler is getting too hut to remove the heat supply
 
D

durhamplumber

Most of the radiators dont get upto to temperature until 2-3hours after the boiler fires and then another 1-2hours for the room to heat up.
Something is seriously wrong somewhere..That is no good to anyone
 
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Do you have a manual or automatic bypass valve? I had a similar problem on my system with a manual bypass valve, i'd actually opened it up to try to fix a similar issue but made the problem worse. I wound it fully closed and then opened it by about 4 turns, that made the radiators get red hot within minutes when the boiler and stat were turned to max!
 

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