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Boiler Blog - Herts Boilers

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Boiler and Heating Technical Blog

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    1. "My boiler is lossing pressure, and my engineer found this!"
    2. Radiators in added extensions
    3. Ceiling lights in a bathroom without RCD protection, is it C2 or C3?
    4. What is the correct hot water temperature setting on a combi boiler?
    5. I have an unvented hot water cylinder, should I time the hot water on periods to save a bit of gas?
    6. For a hot water cylinder, what is the correct temperature setting?
    7. Turn your immersion heater on for hot water while waiting for boiler being fixed
    8. Do I need a new 38kW boiler?
    9. Megaflo unvented cylinder - how to regenerate an internal air gap?
    10. When I turn on my central heating, it is not on, what are the possible causes?

1. "My boiler is lossing pressure, and my engineer found this!"

It is on a Ideal Logic boiler, someone sent us this video:

logic_hex_leaking

After opened the top burner, this aluminium heat exchanger is jetting water to the boiler ceiling. Obviously this heat engine was replaced late, an expensive job through.

(Last edited on 09/05/2021)

2. Radiators in added extensions

For a newly added extension, it is very common that builers T off new radiator connections from a nearly existing radiator's flow and return, instead from main backbone. This offen causes radiators in externsions are not as hot as others.

(Last edited on 09/05/2021)

3. Ceiling lights in a bathroom without RCD protection, is it C2 or C3?

It all the ceiling lights are higher than 2.25m in a bathroom, these lights are not in the special location (zone 0, zone 1 and zone 2), so general and non-bathroom rules should apply them, hence it is C3 not C2.

(Last edited on 10/05/2021)

4. What is the correct hot water temperature setting on a combi boiler?

DHW setting 1It should be 100% or at least above 70% of the full scale. Hot water on its own will give burnt hot water which one can’t take shower directly, and a portion of cold water is also required at the tap to give a right temperature mixing for showering or washing.

Particularly on old combi boilers, it isn’t always stable if you set hot water temperature at the boiler to 30% or so. It often gives a hot and cold temperature cycling.

DHW setting 2So the correct way is to set hot water at combi boilers to full or high, and get hot water mixed with cold water at the tap.

(Last edited on 13/06/2021)

5. I have an unvented hot water cylinder, should I time the hot water on periods to save a bit of gas?

A modern unvented hot water cylinder (white hot water storage tank normally in upstairs airing cupboard) is very energy efficient. That means, it has very little heat loss while storing hot water. It is also not as warm as before in the airing cupboard compared with an old type of vented hot water cylinder.

When hot water temperature reaches 60C to 65C degree inside the cylinder, the boiler stops heating hot water, no gas is wasted even hot water is still on at the programmer.

Total amount of energy being used for hot water is mainly determined by how much hot water your family has consumed, not by the on and off time.

(Last edited on 17/07/2021)

6. For a hot water cylinder, what is the correct temperature setting?

It is 60°C to 65°C. There are two reasons:

  1. At this temperature legionnaire disease bacteria will not survive. This is also a building regulations' requirement.
  2. Hot water at 60°C can’t be directly used in most cases as it is burnt hot. It is designed to add another portion of cold water to make water output temperature to suit washing and showering. In such case, you get more amount of meaningful hot water.

So it is wrong to set cylinder stat to 45°C.

(Last edited on 17/07/2021)

7. Turn your immersion heater on for hot water while waiting for boiler being fixed

Immersion heaterThere are four major heating / hot water systems in this country:

1. Vented or open vented system (head cisterns in loft space)
2. Combi boiler system
3. Un-vented system (Megaflow, with pressure gauge)
4. Thermal stores (Powermax or Gledhill cyinders)

If it is a combi boiler, you have to wait for the boiler to be fixed to supply hot water again.

But if your home has one of other three systems, you might have an electrical element called "immersion heater" to heat up hot water inside your hot water cylinder or thermal store, which will give you hot water but no central heating.

Immersion SwitchThe left picture is a typical immersion heater switch. It is usually off, so you need to switch it on for hot water backup.

There are three reasons for immersion heaters only being used while you have a boiler breakdown: 1. electrical price is expensive than gas. 2. immersion heaters are less powerful than gas boilers. And 3. you don't want your boiler pump or fan seized after a whole summer.

(Last edited on 23/07/2021)

8. Do I need a new 38kW boiler?

It depends on the boiler type. If it is a combi boiler, the answer might be a yes, as instantaneous hot water from the boiler is requiring a high consumption of gas burning.

But if it is non combi boiler, eg a heat only boiler or a system boiler, the system has a storage hot water cylinder, the hot water is pre-heated by a mild power of the boiler output, so the calculation is adding 3kW to 6kW for hot water cylinder on top of heating requirement.

For heating calculation, it is important that one don’t count the number of the radiators, it is the heat loss of the house which matters!

Rule of thumb, we need about 10kW for a 100 square meter house, for such a size house, we need a system or heat only boiler of 16kW.

The calculation is: (a). for old houses without modern insulation, each square meter of the floor plan needs about 0.1kW. (b). for modern houses or flats with good insulation, each square meter only needs 0.04kW.

Incompetency of heating engineers is often shown by wrong calculations. Over sized boilers will not only cost more to purchase, also need bigger gas supply pipes. More importantly, it often causes boiler to cycle, hence reduce its lifespan.

(Last edited on 16/08/2021)

9. Megaflo unvented cylinder - how to re-generate an internal air gap?

(Last edited on 27/08/2021)

10. When I turn on my central heating, it is not on, what are the possible causes?

Firstly if you don’t have hot water either, it is likely the boiler is faulty. Try to note down any error code or faulty lights and call a boiler breakdown engineer, after a check thant you don’t run out gas at a pre paid meter.

If you still have hot water, it is sometimes that boiler is fine but one of following heating controls is in need of attention.

Pressure gaugeMake sure the boiler has a right system pressure, if it is a combi or a sealed system, press here for a top up method by Herts Boilers. Most of combi boilers have an auto stop mechanism if the system pressure is low but Worcester and Viessmann boilers don't have this protection.

gw_energySome modern boilers have a sophisticated control strategy. The left picture is a latest Glow worm combi boiler, you need to turn heating on at the facial for heating, although heating on is a default setting. We did have some call outs in which tenants had played with boiler setting and ended up with Glow worm boiler heating off (no radiator symbol).

Vaillant knobsTurn your heating knob at the boiler to a position around 80% to 90% of the full scale, ie about 60°C to 70°C. For a traditional on/off control, it is a big no to set heating output at the boiler to lower than 40°C. Some boilers now have re-commendation position marked with a reference (E) or physical stop.

wb_buttons Turn heating output at the boiler to 60°C to 70°C as mentioned above. Some newish boilers (Worcester etc) have button type control input, only until you press them otherwise you don't know what the setting it is. If you set it heating here at 30°C you will never get your heating on.

Check if you don't run out batteries on RF room stat (radio frequency or wireless). After a long summer and after a long period of connection loss, you might also need to re-bind the stat with receiver again. Find stat's manual, paper based or get it by a Google serach, and do it yourself if you can. We will charge a callout if we make this kind visit.

Other than above five, you will need to call a heating engineer in.

(Last edited on 04/10/2021)

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