Hydronic heating system question

[Bob_A]

Hello all,
We have a hydronic heating system (3 zones) on our boat with a relatively new Espar D5. Please see the pic attached. Someone has installed these Watts 150psi pressure relief valves perhaps as an auto bleed above the supply and return to the Espar. These are located adjacent and above the aft cabin coil but below the system expansion tank. Therefore not the highest point of the system (the tank is). For context they are above the salon coil and possibly at or slightly above the fore cabin coil. These Watts valves dont look at all marine to me and they are failing and slowly emitting coolant without the system running and will leak with any warmer change in ambient temperature.
My question is, should any auto bleed be in this location at all given the tank is highest and if it is advisable what devise would be recommended?
I do not see a bleed screw on the Espar but I do see where the coils bleed.
Thank-you

[Captain Kirk]

Hi Bob

We have a hydronic heating system on Sand Dollar, but its a Wabasto furnace not an Espar. In any case I believe our installations will be very similar. We have 4 zone system, one in the aft cabin, one under the galley sink that blows air into the galley and into the salon, one under the basin in the head that blows both into the salon and into the head. The fourth one is under the forward berth and has two outlets, either side of the berth. Each of the coil radiators has the ability to be ducted off both sides providing the dual outputs on 3 of the 4 radiators.

We don't have the relief valves you have, but the expansion tank has a pressure cap like a radiator cap. Not sure if this equals the function of your 2 valves. The radiator cap on the expansion tank is the highest point in the system. The system was installed in 2006 by the PO and we've had the boat since 2016 and have never had a leak of any type..... knock on wood.

I have attached a schematic drawing of the system that I put together a year or two after we purchased the boat. You will also note that either the hydronic system or the engine heat can make domestic HW with the use of the interposing heater exchanger, item 4.
Hope this helps at least a little.

[Bob_A]

Thank-you Kirk,
Yes very similar. Ours to utilizes the heat exchanger isolating the engine coolant from the heating system coolant.
Nice schematic. I'm positive the Watts valves shown on ours do not belong. They served for awhile, or didn't hurt, but now that they leak they are in need of removing.