faq

Frequently ask questions

We try to answer questions that are asked everyday by our customers. Alwasy remember no question is stupid, only an answer that is not correct is stupid. Please read through our faq's on heating and if you still have questions them please contact us so that we can answer them for you.

Have you bled your radiators recently? This removes pressure from your system by venting air and needs replacing with water.


Does your heating system have a leak? If there is a leak on a radiator valve, radiator or on the system pipe work the pressure will drop as water escapes necessitating topping up the boiler.


Has the Pressure Relief Valve opened and now not closed.


If the boiler is over pressure due to overfilling or some other fault the over pressure safety relief Pressure Relief Valve will open. This is usually at 3 bar on modern boilers.


Once this valve has opened often they never re seal themselves correctly letting water pass from your boiler. A pipe runs from the pressure relief to outside and a drip from this will be evidence of a dripping pressure relief valve.


The pressure relief will often drip as a consequence of a failed expansion vessel in the boiler.

If there is a drip, consult your Gassafe engineer who will diagnose the fault.


The boiler has an automatic air vent. This is designed to remove air from the system. This will have the same effect as bleeding a radiator.

This could be evidence of an internal fault within the boiler and there are a number of potential causes which will need investigation from you Gassafe engineer.


A common reason for overpressure lies at the hands of the homeowner in that they overfill the boiler.


As pressure rises with temperature the boiler should only be topped up when cold so that the boiler is giving a pressure reading cold. The boiler should then be carefully topped up to the 1 bar mark. This can vary on other sealed systems and should be checked out by a professional heating engineer.

Your boiler will often have an internal mechanism to enable pressurization known as the filling loop. Where the boiler does not have an internal mechanism an external filling loop will have been provided on the heating system.


Many things can cause a boiler to lose pressure, from someone bleeding radiators to the boiler over pressurizing and automatically venting. You may have a leak on the system that you cannot see, which is below floor.


If your boiler is losing pressure regularly causing you to have to top the pressure up frequently, it is recommended that you seek an inspection at your earliest convenience. You many have a problem that could damage other parts of your heating system that is causing the issue at hand.

Found on older open vent hot water and heating systems typically the larger tank is the cold water storage cistern and supplies water to the hot water cylinder and traditionally the cold water taps except the cold tap in the kitchen which was usually on the cold main.


The cold water storage cistern also provides a temperature and pressure relief outlet for the vent pipe on the hot water system.


The smaller tank is the feed and expansion cistern for the primary heating circuit and is used to fill your heating system rather than the filling loop[ used on the modern pressurised systems.

Most definitely yes. Without a room thermostat your boiler will try and heat the water in your primary heating circuit to the temperature set on the boiler thermostat. It will repeatedly turn on and off maintaining that set temperature this is known as cycling.


If you have a room thermostat once room temperature is achieved the boiler will turn off. The room will maintain temperature for a period of time and the boiler will only re ignite when the temperature has fallen back to the temperature at which the room thermostat is set to call for heat. During this period of time the boiler is not cycling and therefore gas is not being used inefficiently.

Boilers prior to 2005 were none condensing boilers with the flue gas temperature in the 130 / 150 degree C range.


The condensing boiler has a more efficient heat exchanger taking more latent heat from the flue gasses reducing the flue gas temperature to the 50/60 degrees C range. This is below the dew point and condensation forms in the boiler heat exchanger. This condensate is acidic and has to be disposed of safely.

Firstly ask your local water authority to check your supply. You need to ascertain that there is sufficient water in the main supply before considering your options.


If the water authority confirms there is sufficient supply. Is there a blockage on your service pipe between the main and you house? You will need an engineer to check out the flow rate. If there is a blockage you will need to repair or replace the service pipe. This is common where the service pipe is Lead which should be replaced.


If the cold water supply from the main meets the local water authority minimum criteria but the pressure and flow is still too low to operate a modern heating and hot water system then you can consider a pumped solution.


It is against regulations to pump directly from the main. It is therefore possible to install a home boost unit which has its own storage tank and pump to produce a serviceable cold supply in the house to facilitate the use of a combi boiler, unvented cylinder and showers.


It is possible to use a simple boost pump unit up to 12 litres per minute after your cold stop cock. 12 litres per minute however is barely sufficient for most modern systems.

MTS Heating Services installs a system filter on every new heating system and new boiler. Indeed it is now part of Building Regulations to do so.


The filter is usually fitted on the return to the boiler and has an integral magnet. This magnet attracts the metal particulate in your heating system stopping it from entering your boiler and blocking up the boiler and wearing out the pump..


Many boiler manufacturers now offer extended guarantees if you use their own system filter.

Usually this is because there is air in the top of the radiator and it needs bleeding to let the air out.


It sometimes can be an indication of a blocked or dirty system.

This is a typical symptom of a failing pump. Hot water is less dense than cold water and therefore likes to rise. If your circulating pump is failing it cannot force the water to the lower radiators and the hot water rises to the upstairs radiators.


If your pump is ok it may be that your heating system is out of balance. Your heating engineer should be able to assist you with this.


It may also be the case that your heating system is dirty and sludge is affecting the circulation.

An unvented cylinder is fed cold water direct from the incoming cold main. Ideally the incoming main flow rate should be at least 20 litres per minute. The advantage of the unvented cylinder is that the hot water flow is at or near the same rate as the incoming cold water.


Unvented cylinders can be used in conjunction with solar heating systems both wet and Photo Voltaic (PV) as they have the facility for two heating coils and also two immersion heaters.


The pressure of the water is usually restricted to 3 bar by the unvented cylinder pressure reducing valve.


The unvented cylinder has a number of safety controls and can only be installed by a qualified engineer. This qualification is separate to the normal gas qualifications and you should ask your installer if they hold “G3” which is the relevant qualification for the installation of hot water storage systems under section G3 of the building regulations.

There are a number of reasons why you may have poor hot water flow and pressure.


The most common reason is that the hot water is generated in an older open vent low pressure hot water cylinder where the hot water pressure is generated by the height of the cold water storage cistern above the hot water cylinder this is known as the “Head”.


In some cases storage above the property, typically the loft, was not available for example in a flat and a combination cylinder was used where the cylinder has its own cold water tank to supply hot water. In this case there is minimal head and little hot water flow as a consequence.


In the case where you have an old low pressure system you could consider


  • a. A hot water/shower or whole house pumping arrangement.
  • b. A combi boiler
  • c. An unvented hot water cylinder

It is best to take advice on the best course of action as this will depend upon the incoming mains cold supply and also your budget!


If you have a combi boiler and the hot water flow is poor this could be as a consequence of poor incoming mains supply. It may also be indicative of a fault or blockage within the boiler.


This is particularly common in hard water areas. Limescale blocks up the channels in the plate to plate heat exchanger that makes the hot water.

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