Keeps going hot and cold

Hi guys.

I've just moved into a house which has a Boilermate 2000 and a Gloworm boiler.

When you run the hot tap, the water keeps going hot then cold all the time. Flow is strong and consistent.

I've just searched on line and found two things to check, one is the filling tank placed on top of the cabinet, the other is the hot water pump on the right handside to the heat exchanger, is there anything else I could check?

Craig.

I'm fairly sure none of the three pumps are working.

Top cistern tank is ok.

Actually boiler pump is working, not sure about heating pump, heat exchanger pump intermitent while tap open.

If you are in hard water area then it could be PHE. It is not difficult to change it. You can buy it online for arounf £100, but before buying take it off and look inside, it will be obviouse if blocked with scale.
How to remove:
You don't need to drain whole system, may be around 20 liters. Isolate main water feed from filling expension tank. Close valve on top of HW pump. Connect pipe to outlet over that valve and open valve on outlet.
Ah, and isolate cold water. I usually do whole house and open some taps cold and hot.

Did you ever get this resolved?

Having had a similar problem three times in 15 years, my experience is that one of the two sensors could be faulty.

PHE return sensor - Stock code GT153
D.H.W. sensor - Stock code GT153


It is often recommended to change both at the same time. I have only ever had to turn off the main stopcock coming into the house and wrapped a towel around the sensors as I removed them. Very little water escapes.

To be honest, they need changing again but for some time, we have just switched the immersion on before using the shower as that has kept the temperature constant. Just need to remember to turn the switch back to normal afterwards!

Lazy I know, but it works.