Boiler in trouble - replace with system or heat only

[Dan Robinson]

Size the boiler to the house. Why do you think you need a 28kw boiler?

Also, that manual might be written for standard efficiency boilers.

 

[busydad]

It was just what my heating engineer stated last time he was in to do a service. I assumed because it is a big house basically with lots of rads. However my glow worm is something like 14-17kw and manages fine. Therefore something of the same order should do in that case? (even if get an unvented cyl in the future)? My knowledge is limited but do understand the kw needed is much lower than would be needed for a combi for example.

Edit - my current boiler has max output of 17.59kw, so for example a baxi 19kw heat only would be sensible? Or even a 16kw?

 

[Mottie]

Very much depends on the installation.

My pump cost me around £95 (Grundfos) and took me around an hour to fit and that included picking it up from my local plumbers merchants. I could have bought a cheaper make for around half that price and no doubt that's what you'd get if you got a plumber out - to most people, a pump is a pump. My old pump lasted nearly 15 years.

 

[Dan Robinson]

Great. And your situation is going to be the same as the other 30 million Heating systems around the country? Have you worked on many thermal stores?

 

[McCombi]

Your system mate has two pumps built into it.

One is to circulate the hot water from gas boiler to heat the thermal store tank and other is to circulate hot water through a circuit through the store to the radiators.

So a regular/heat only is used as pump is part of systemate. A system boiler has pump built in to it so not affective as you already have pump on systemate for this purpose if that makes sense?

 

[Dan Robinson]

One could argue that a modern system boiler with the pump duty linked to the DT of the burner is preferable to a fixed speed affair bolted to the store using (usually in my experience) those crappy ball-a-fix pump valves .

 

[McCombi]

One could argue that a modern system boiler with the pump duty linked to the DT of the burner is preferable to a fixed speed affair bolted to the store using (usually in my experience) those crappy ball-a-fix pump valves .

Certainly doable. Was going to add it to my post but didn't want to add extra confusion

 

[Dan Robinson]

Certainly is... Did it to my store when I had it operating.

 

[busydad]

Your system mate has two pumps built into it.

One is to circulate the hot water from gas boiler to heat the thermal store tank and other is to circulate hot water through a circuit through the store to the radiators.

So a regular/heat only is used as pump is part of systemate. A system boiler has pump built in to it so not affective as you already have pump on systemate for this purpose if that makes sense?

Yes, understand thanks. Definitely will just go for heat only.
If I replace the thermal store in the future I therefore assume you can get pumps fitted locally to the cylinder in a similar way.

In an ideal world I would replace the boiler and thermal store with an unvented cylinder and system boiler, but because I am without hot water and heat a direct replacement with a heat only boiler and sort out the thermal store at a later date seems like the only real option (in a reasonable timescale).

 

[Mottie]

Great. And your situation is going to be the same as the other 30 million Heating systems around the country? Have you worked on many thermal stores?

No, but it’ll be the same as the OP's if and when he fits and external pump to his heat only boiler instead of buying a system boiler. There was only him asking, not the owners of the other 29,999,999 systems.

 

[busydad]

And just to check, if getting another boiler it should be rated similar (in kW) to the existing boiler? Current boiler has an output range of 14.65 - 17.58kW. If I were to get a Baxi Ecoblue Heat only for example, would either a 16kW or 19kW seem like the most sensible option given that it's linked to the thermal store and the current boiler output? The current boiler is always set to max, so might the 16kW be a little short of output? Indeed if I went for the 19kW, is it possible to downrate the output if it is too high? (I've heard the thermal store can be temperamental if the boiler output is too high).

 

[McCombi]

Yes, understand thanks. Definitely will just go for heat only.
If I replace the thermal store in the future I therefore assume you can get pumps fitted locally to the cylinder in a similar way.

In an ideal world I would replace the boiler and thermal store with an unvented cylinder and system boiler, but because I am without hot water and heat a direct replacement with a heat only boiler and sort out the thermal store at a later date seems like the only real option (in a reasonable timescale).

In future if you wanted to change to uv cylinder, you could setup as what's called s plan system.

Be easier for you to search internet for a diagram of a s plan system than it would for me to explain fully but give you a rough idea.

Heating flow pipe comes off boiler, external pump fitted (only need one on this system as it's pumping direct to radiators and cylinder coil rather than pumping into a store then separate circuit pumping to rads) splits into two circuits which each has a motorised zone valve (2port valve/actuator) one goes to radiators, other to uv cylinder coil, and the heating returns and cylinder return goes back to boiler.

Pushing on programmer for heating, if room thermostat is asking for heat it sends power to 2port valve to motor open the valve, which also makes a switch and sends power demand to boiler.

Like wise with water on, sends power to valve/motor, opens and sends power to boiler.

 

[GasElectricalRepairs]

I agree with Dan and have the same, system boiler to an unvented on an S plan. The system option will be more efficient, less noisy, neater and less problematic.
If going for the heat only, check for bypass and pump overrun etc requirements.

 

[dilalio]

And all under guarantee