Thermal Store Problems

The THERMflow thermal store continues to be one of the most reliable hot water cylinders on the market today, however issues can arise from time to time.

Below contains a guide to a few of the problems which can arise with thermal stores.

If this does not resolve your problem, please contact either your installer or phone McDonald Water Storage Technical Team on 01592 611123 for further advice.

The water at the tap is lukewarm or cold.The thermal store is designed to work best when the store temperature is at or approaching 75°C – 80°C.  While the thermal store can provide hot water at lower temperature storage, the available flow rates and volume will be reduced. Check the thermometer is showing the store temperature is at or approaching 75°C -80°C.  If this is not the case, ensure that the boiler is firing and allow sufficient time for the store to reach working temperature.
The thermal store is at 80°C and the water at the taps is still lukewarm or cold

1. If the store is at or approaching 75°C – 80°C, check that the Thermostatic Mixing Valve is turned to hot.  The maximum temperature of water from the Mixing Valve is 55°C.

2. If the valve is turned fully to hot, check that the flow rate at any outlet (e.g. bath tap) does not exceed 20 Litres per minute.  If the flow rate is above this, then turn the tap down slightly.

3. If Stage 1 and 2 has not resolved the problem a competent installer should check the mixing valve for blockages within the internal filter of the mixing valve.

Not enough hot water and less than 80°C on the thermometer.Check the heat sources and their input in (kW) to the store as this will be lower than the kW output which will result in the store not producing enough heat for the exchanger to provide heated mains pressure water.
THERMflow is set at 80°C but the mains pressure temperature drops quickly when running a tap (e.g. bath)

1. Check with the installer that inhibitor has been put in frequently.  If the DHW Coil is giving an initial heat transfer and then fading this could be a sign of sludge build up surrounding the Heat Exchanger Coil, which will reduce the performance of the store.

2. If Stage 1 does not resolve the problem level of input and output may be affecting performance, this is tested by drawing off the same flowrate of water when the output is lower, such as turning your heating off.

There is a brownish tint to the mains pressure hot water.This could be a symptom with the heat exchanger coil leaking inside the thermal store. An installer should have this tested. If this is the case, pay attention to the Feed & Expansion Tank as the pressure within the store will increase causing the tank to overflow continually.