Potterton Promax Combi HE+ Hot Water Temp Low

[RJPotts]

Hi All,

I have a Potterton Promax Combi HE Plus combi boiler. It was fitted when the house was built about 4 years ago and has been fine until this morning.

I was only able to get a useable temperature for a shower by turning the shower temp to the max position and even then it was lukewarm, certainly not hot.

I checked the temperature on the hot water thermostat on the boiler casing and it was still set to 50'. As it's close to the kitchen sink I was able to see what happens when a hot tap is turned on. The hot water indicator lights to show demand but although the temperature of the water was less than 50' the boiler did not light. Only when the temperature reached 20' did the boiler light and the water warmed. At 40' the boiler switched off, water temp dropped of course and the boiler did not relight until it had dropped to 20'.

After several trials those temps are not consistent, it will sometime switch off at a slightly higher temp than 40, sometimes lower (it has not reached the 50' set on the thermostat). Using the reset switch and turning the power off completely and back on have not helped.

This only seems to be affecting the hot water system, not the heating.

Unfortunately this comes at the worst possible time, as it appears I'm out of a job at the end of the year (

Can anyone suggest any potential fixes please?

Many thanks in advance
Richard

 

[muggles]

Probably the hot water thermistor

 

[RJPotts]

Thanks for the message Andrew!

Any idea if this might be a DIY replaceable part in this boiler type?

Many thanks
Richard

 

[muggles]

Yes, you can DIY it. First thing to do it check its resistance when cold, should be about 12 ohms, if it isn't it's knackered. Then check resistance as it heats up, should increase.

Part number 5114725 if you need a new one

 

[RJPotts]

Hi Andrew,

Just wanted to say a huge thank-you!!!

I've just replaced the sensor and have hot water again

The old sensor gave a reading of 1.8 where the new one was indeed within a hairs breadth of 12. It shows signs of very slight water seepage so I've made sure to clean up the mating surfaces and have tightened it a little more than what the old one was.

Thanks!
Richard