Central heating but no hot water?

Question

I have a Potterton (Powermax) 155x combi boiler. We currently have heating, and get about ten seconds of hot water under the shower before it disappears.

We have had an engineer out and he fixed an initial problem where the boiler was continually locking out. For this he needed to replace the PCB. He also replaced two other parts - the water level valve? and another valve.

Now however we still have the hot water issue. Any ideas?

Also, if someone could tell me exactly what the switches on the 155x do that would be great - there is a "Store" 0/I switch and another switch with a little radiator symbol. Considering I tend to run the boiler on timed operation, where should these be set?

Any help greatly appreciated, three weeks of cold showers this is not fun!

Answer 1

Could be the diaphragm in the pressure differential switch which activates the change over from heating to hot water and also fires the boiler when the heating is not on. If this diaphragm has a small split then it slowly allows the pressure to equalise on either side of it thus switching the hot water side of the boiler off. Has the time the water runs hot for been reducing over the past few weeks? if it has this is almost certainly the answer. hope it helps.

Answer 2

It could be the hot water flow valve in the boiler is faulty. If it is, you have to replace them, they are not repairable. As for what you said about the PCB , When the engineer tells you or anyone else that it needs replacing, make sure that you keep the old one. I say this because there is a scam going around with PCBs where by the engineer takes the one that he says is faulty and goes off with it to get another. What some are doing is driving around in their van for half an hour then coming back with the same PCB and fefitting it at an extorianate price. The price for a new PCB from a merchant is about £35. So people beware.

Answer 3

There something definitely wrong with your Central heating system if radiator water is coming through your taps. Central heating is designed so that Radiator water is heated and then recirculated through the system radiators this water should never encroach into the Hot water pipes as it will severely contaminate a Clean fresh water supply. A valve called a "Zonal valve" is fitted to a Central heating system to prevent cross contamination, it is probably stuck or broken. Have a central heating engineer look at it, he may be able to free the mechanism or replace it, it's quite an easy job to do and not very expensive. Under no circumstances drink water from the tap until you get the problem fixed.

Answer 4

Assuming there is no fault on the boiler, it sounds as though you just have the water heating function turned off ! The inital 10-seconds of hot water is coming from the heat generated when the heating is running, without the burner running for the water side this soon dissapates.

Answer 5

Oh lol the replace pcb line, good one, did he just bill you for it, or actually blow yours up for you. What other items that you buy need new printed circuit boards a year or two into their life?.
I would steer well clear of that plumber in future.

You should be able to download a manual from the potterton website to tell you what the switches do and possibly look for a potterton approved engineer.

Answer 6

Possibly the diaphragm has burst in your boiler, i have a combi boiler and had this problem 2 years ago and it was the diaphragm and the pipes had furred up with limescale which didnt allow the hot water to get through.

Answer 7

The farther north you are the less you need hot water on demand. You can add a small electric hot water down line just for the showers. When it comes the home tech keep it simple or rent .

Answer 8

Hope your thingy is up and running after all them cold showers lmao

Answer 9

it looks like you might have a faluty hotwater temp stat,