Herz biomass boiler technical support

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Are you having a issue with your herz biomass boiler, then you have come to the right place to resolve your problems. A brief overview on a typical biomass system will be discussed.

Here  each boiler range will be discussed providing information on system faults and how they can be rectified.

With several years experience on the HERZ boilers our knowledge is worth sharing, If you need a site visit then get in touch and we can get your system running again.

Biomass system design-boiler to buffer

For a biomass system to work correcly the initial design has to be correct. THe boiler size is the starting point, if this is undersized then the property will be cold and the boiler itself will constantly be in run up phase working at 100%.This means the boiler is constantly working at maximum output, biomass boilers should modulate down to around 30% and keep up with demand this way. Oversized and the boiler can modulate too much and go through the start stop process several times a day, this is not efficient as this is when the boiler uses most fuel and emmissions are poor.

Correctly sized pipe work and pump sizing is important, this determines how much flow rate you can achieve round the system. You generally aim for a delta T of 10 - 15 degrees, due to the minimum return temp on most biomass boilers being 65 degrees to prevent boiler condensation your flow temp will be at 75-80. to keep the return temp at a minimum of 65 a 3-port mixing valve is used to mix the flow and return temperature. Anyway if the pipe is undersized your delta T could be 20 -25. This can cause over temp issues with the system if not set up correctly. YOu could turn the pump up to its max output but in most cases this is not sufficient as its been specified to the boiler. If you are having these problems with your existing system the Solutions are - 1.Firstly check all strainers and make sure there is not a blockage in the system,2. have someone competant and trained check the commissioning settings and sytem- It is possibe to derate the system slightly to a lower KW output only if the system heating requirements allow this, 3. increase pump size(cheapest option) 4. change pipe work as a final option. you can find our biomass serive prices by clicking on the link.

Flue Design - Eac boiler manufacurer should have standard size and height guidelines, this is to achieve the correct amount of draw measured in pascals,taking the positive pressure out of the boiler and sending the emmissions through the flue, other considerations should of been taken into account, ie  regs- basically the surrounding area to the building. You should also have a flue draught stabiliser fitted to the non static part of the flue, and relevant access points for cleaning and a flue drain at the bottom of a T.

Biomass control process

  There are a few stages to a boilers operation. On initial start up the boiler goes through an ignition phase and a pre ventilation process thus preparing the boiler for a cold/warm start depending on combustion temperature. then a scorch phase is started which creates a fire on an even bed of fuel followed by a run up phase, this is the boiler running at 100% to achieve a commission set boiler temperature, once this is achieved the biomass boilergoes into control phase with the aim of modulating down to 30%, this is when boiler is working most efficiently and cost effective. the system will then shut down once the target temperature is reached within the buffer tank(usually bottom) via a PT1000 sensor.


Possible issues can be related to fuel quality and I am sure you have heard this one a lot, but yes fuel can cause issues with burn backs if the fuel is too dry on wood chips - 15% moisture content or lower. If the fuel is too wet then the boiler can struggle to maintain maximum heat output.

Wood Pellets- Too much dust can cause issues too. They can arrive very dusty from certain suppliers so choose your supplier carefully and always go for a quality product not the cheapest. Wood pellets can become broken down when the fuel is blown into the fuel store, there is usually a pellet mat fitted to minimise the breakdown of pellets so if this is not fitted then you will need this fitted immediately.

Ensure there are no contaminants within the pellets, this can cause clinker build up if the pellets are not to the correct specification causing more breakdowns with the system. Ash discharge faults with the augers and can be quite costly to replace.

Herz boiler faults and issues

There are many different models of herz boilers, we have worked on them all over the past 7 years. So as well as the latest T-control models and Biofires we also offer support for the older range covering the 3-phase firematic on a biocontrol board, Biomatic's and biocontrol pelletstars.

We have all the latest software for every model and understand the boilers inside out with the knowledge to diagnose and fault code.